Similar in design to the D'deridex-class warbird, the Valdore-type was a large, fixed-wing vessel. Ships of the class had a color scheme of dark-green or brown.
With a wingspan roughly 900 meters wide, the vessel featured a large section extending forward to create a down-sloped head shape. Warp nacelles were connected at the end of each wing with impulse engines mounted aft. The hull was marked by distinctive "feather" shaped plating. (Star Trek Nemesis)
Ships of the Valdore-type featured several forward-mounted disruptor banks, located on each wing and some on the forward section of the ship. It had at least one forward torpedo launcher, able to fire four torpedoes for each recharge. (Star Trek Nemesis)
The command center of the Valdore-type consisted of a roughly circular room, distinguished by several console positions. The room had a dark metallic-brown color scheme, with green graphics on the computer monitors.
With computers lining the rear bulkheads, a center seat or command chair and free-standing console were flanked by two additional stations. The Valdore-type also had a viewscreen, which was oval-shaped. (Star Trek Nemesis)
In the screenplay of Star Trek Nemesis (both the first draft and the shooting script), the vessels of this type were referred to merely as "Romulan Warbirds", with no indication as to whether they were intended to be of the D'deridex-class or a new type.  Although the film's producers could have feasibly reused the D'deridex-class from Star Trek: The Next Generation in Nemesis, they were insistent about instead wanting a brand new style of Romulan warbird in the movie. (Star Trek: The Official Starships Collection, issue 31, p. 14) In his blog, Concept Artist John Eaves has stated, "It was always called the Valdore-class in what we were doing! and this was the signature Valdore! [....] As far as I know, it had no other class name."  
The job of designing this type of vessel, as a new version of the Romulan warbird, was assigned to John Eaves. He decided to base the Valdore on a couple of vessels that had been created years previously, such as the Klingon Bird-of-Prey from Star Trek III: The Search for Spock, of which he was a long-time fan. "I thought, 'Well, I'll take that and rearrange it a little bit,'" Eaves recalled. (Star Trek: The Official Starships Collection, issue 31, p. 14) He actually proceeded from the then-behind-the-scenes assumption (based on an early draft of the script) that the Bird-of-Prey was a Romulan ship stolen by the Klingons. Eaves based his design of the Valdore on a supposition that the Bird-of-Prey had been a typical configuration of Romulan vessel and that the Klingons had either bought or stolen the Bird-of-Prey or its technology. "From there the Romulan Warbird Valdore could easily fit into the design realm of what was seen before, only heavily modified," he reasoned. 
Another starting point that John Eaves took inspiration from, while producing concept artwork of the Valdore, was the D'deridex-class, which had been designed for TNG by illustrator Andrew Probert. "I ran to Andy's ship for an architectural lineage to use as the cornerstone for the renderings," Eaves stated.  He was inspired by one aspect of that design in particular. "I took the cowling from the front of the TNG Warbird [...] and incorporated it with my new kind of stylized Bird-of-Prey," he reflected. "So, it was kind of a progression of the Bird-of-Prey and Andy's Warbird." (Star Trek: The Official Starships Collection, issue 31, p. 15)
While John Eaves was busy illustrating concept sketches of the new Romulan warbird, his boss, Production Designer Herman Zimmerman, also commissioned Illustrator David Negron, Jr. to devise some concept designs for the same vessel. He worked independently of Eaves, at the other side of the Paramount lot, and it was hoped that this arrangement would result in a variety of different looks for the ship, from which the final design would be selected. "David came up with a very aggressive 'T-tailed' design that incorporated some of the lines from Andy Probert's TNG Warbird," said Eaves. "He compacted the design, and I really liked the interpretation he came up with." (Star Trek: The Official Starships Collection, issue 31, p. 15; )
John Eaves included wings in his versions of the craft, making the new warbird seem raptor-like. In his initial sketches of the Valdore, however, he experimented with different wing positions. For example, his second concept pass featured upswept wings. (Star Trek: The Official Starships Collection, issue 31, p. 15; ) Regarding that rendition, Eaves remarked, "It almost had a Batman feel to it; that's why I ditched it!"  Eaves ultimately filled a single page with three or four ideas of how he imagined the new warbird might look. The page was then taken to an art meeting, at which Herman Zimmerman and the producers chose one of the designs. "Herman Zimmerman came back with a circle around one of the drawings that said they wanted to see more on that one," Eaves continued. (Star Trek: The Official Starships Collection, issue 31, pp. 15-16)
As requested, John Eaves created a few more detailed sketches based on the chosen design, including some in which the exterior panels featured a feather pattern. He based these on books about birds such as hawks and condors. "It was really fun," he enthused. Eaves noticed, however, that the feather patterns looked too similar to that on the panels of the Klingon Bird-of-Prey's hull. "So I took all mine off and redid them so they would be different," Eaves noted. Once he had devised a feather pattern for the warbird that he felt was unique enough, Eaves focused on the underbelly details and the warp nacelles. At first, he placed a pair of secondary warp nacelles on the underside of the ship. This was to further the vessel's original backstory that they were an unusual type of nacelle, to be used only while the ship was cloaked, so as to mask the craft's warp trail. Eaves felt these nacelles spoiled the sweeping lines of the vessel, so he ended up moving them to the ends of the outer wings. "I [...] started working in a subtle arched bi-wing," he explained. "The extra wing added a good break-up to the forward view and helped tie in with the design flow that Andy had come up with for TNG." (Star Trek: The Official Starships Collection, issue 31, pp. 16-17)
After final approval of the design, the Valdore was built as a CGI model at Digital Domain by Andy Wilkoff. Eaves was delighted to collaborate with Wilkoff and encouraged him to add his own creative input to the design. (Star Trek: The Official Starships Collection, issue 31, pp. 16-17) "He did a lot of really beautiful work, too, adding personality to the ships that wasn't there in the drawings," Eaves commented. (Cinefex, No. 93, page 101) In fact, he cited the Valdore as "one of my all time favorite" ships, adding, "and the modeling work was beyond incredible." (Star Trek: The Official Starships Collection, issue 31, p. 17)
The bridge of the Valdore was a redress of the bridge of the Enterprise-E. Only a few pieces were retained from that configuration of the set. Those which were kept were repainted, recarpeted, and rendered unrecognizable. Because the same platform was used for both versions of the set, though, the Romulan version still had the same shape as the Enterprise's bridge. The Valdore's command chair was represented with a Klingon bridge chair that had been used since Star Trek: The Motion Picture. The viewscreen of the Valdore was a reuse of the Son'a version from Star Trek: Insurrection. ("Build and Rebuild", Star Trek Nemesis (Special Edition) DVD) Chairs from the USS Voyager were incorporated into the set, as was a Cardassian computer console (at the center of the room) and two computers recycled from the Klingon Bird-of-Prey dating back to Star Trek V: The Final Frontier. (citation needed • edit)
The Star Trek Customizable Card Game refers to the Valdore-type as the "Norexan-class".
The Star Trek: Titan novels from Pocket Books classify the Valdore-type as the "Mogai-class", after a man-sized predatory bird native to Romulus. Star Trek Online does so as well, though it also features an upgraded version which is referred to as the "Valdore-class".
According to the Titan series, the Valdore-type ships are smaller than the D'deridex-class vessels but are newer and more heavily armed, with more advanced weaponry. This may explain the significant difference in the appearance of this vessel's weaponry compared to that of the D'deridex-class, which is portrayed as firing bright neon green torpedoes and disruptors. Also according to the Titan series, the Valdore-type significantly outnumbers the D'deridex-class in terms of numbers within the fleet.