They were approximately the same size as a Danube-class runabout, as one was capable of fitting on a landing pad, and could carry at least three passengers. Romulan shuttles were also fitted with a cloaking device. (DS9: "In the Pale Moonlight")
Ships of the class
The Romulan shuttle was designed by Doug Drexler at the behest of Gary Hutzel, who, as Drexler recalled, put his request as follows, "It's a brief, almost throwaway shot of the shuttle landing at DS9's mid ring, and riding the elevator down into the station's hangars. We'll need a design for the shuttle, plus the hangar interior… can a guy like you, do a thing like this, for someone like me?" The studio model miniature, which only made one appearance in the entire franchise, was built by Tony Meininger at Brazil-Fabrication & Design. According to Drexler, the pod-like modules appearing in the midsection of the main body, between the nacelle struts, are the passenger compartments.
The model was filmed for its only appearance at Image G, where it was handled by among others Dennis Hoerter.  No motion control photography was utilized on the model, as no in-flight shots were required. Instead, stationary shots were taken of the model inside the maquette of Deep Space 9's shuttlebay, specifically constructed for the episode, and likewise designed by Drexler. 
Nevertheless, the shot did require some work in post-production compositing, as Drexler explained, "It did require compositing. Gary shot every element as its own layer… engine lights, cockpit lights, hangar bay lights… everything. That way, when you get into comp, you can adjust any element you want. I'm nearly certain it's 35mm. The smaller camera would make it easier to get in close." The Romulan shuttle was the last full-fledged physical studio model ever built for a Star Trek television production, as CGI modeling was used exclusively afterwards. The reason why a physical studio model was built in this late stage, when CGI was already commonplace, stemmed from Hutzel's preference to use traditional visual effects techniques over CGI.
The following information of specifications and defenses comes exclusively from the Star Trek: Deep Space Nine Technical Manual (the length corresponds with the aforementioned comparison chart done by Gary Hutzel and Larry Nemecek):
- Production Base: Unknown; Romulan Star Empire
- Type: Long-range warp shuttle
- Accommodation: Fifteen plus officers, crew, and troops (est.)
- Power Plant: One artificial singularity-drive warp core feeding two nacelles; one impulse system
- Dimensions: Length, 24.23 meters; beam, 15.98 meters; height, 6.57 meters
- Mass: 142.31 metric tonnes (est.)
- Performance: Warp 9.6 (observed)
- Armament: Six ship-mounted disruptors; two photon torpedo launchers
In Star Trek: Armada II, the Romulan shuttle model was reused as the Kestrel-class; however, as an assault vessel carrying 500 Romulan troops, it would have to be significantly larger than the shuttle featured in the show. Star Trek Online also identifies it as the Kestrel-class, designated as a runabout.