Basic room model

You can use empty box as a room model from Assets May be that can help to do your task,Or build it from sctratch with vertical and horizanta plane.

start with this one https://helpx.adobe.com/dimension/how-to/apply-2d-vector-art-to3d.html?playlist=/services/playlist.helpx/products:SG_DIMENSION/learn-path:get-started/set-header:ccx-designer/playlist:orientation/en_us.json&ref=helpx.adobe.com

no there is not a room model because the room is a background image and the models are what you put in front of that image... so for example, go into any real room and take a photo of it then use that photo as your background image

p.s, there are some nice free models on Adobe stock