Romulan D7 Battlecruiser.

Here are some images of Polar Light's 1/1000 scale Romulan D7 Battlecruiser.
From Wikipedia"
In the original series, at least three starships of the Klingon D-7 class were used by the Romulans. (This came to pass when a fire at NBC's studio warehouse destroyed the only existing Romulan ship model (the 2260s Bird of Prey), necessitating re-use of the surviving Klingon props.) Novels (as well as fans) have speculated that these vessels were given to the Romulans during a brief alliance with the Klingon Empire against the Federation (in exchange for which, the Romulans provided the Klingons with cloaking technology), though this is non-canon and has never been confirmed onscreen. The Romulans refitted the D-7s in their service with cloaking devices and the Federation occasionally referred to Romulan controlled vessels of this class as "battlecruisers."