GTA San Andreas
In Grand Theft Auto: San Andreas, the Grotti Showroom is inaccessible to the player and plays no role in the storyline whatsoever.
In Grand Theft Auto IV, the showroom has a little more to offer. The only car they sell is a Turismo which the player can steal and either drive out the double doors or out one of the many breakable windows.
The glass double doors bear a big Grotti logo on them, there are also Grotti logos on the walls. There is a spiral staircase at the back of the showroom which leads up to the next floor. Both floors contain Turismos which are on display. There are pedestrians and workers around the showroom, presumably looking at the cars or working in the showroom. There are windows all around which can be broken if hit or shot.
The windows are visible (obviously) around the whole of the building and there is a roof over the top of the double doors that can be walked on by going up the interior spiral stairs, smashing the window and walking onto the roof.
The showroom plays a role in the history of The Lost and Damned during Shifting Weight, where Johnny, Malc and DeSean are blocked by NOOSE Patriots and Police cruisers from all sides, and the only way to escape is by crashing into the windows of the showroom, and successfully coming onto Union Drive East.