If you think that the room you have just designed can be useful in the next future, you can save it in the Room Components (also called Rooms Templates) and use it again as a room shape for a new project. You can proceed saving the room template by clicking the right mouse button inside the room, and selecting the command Add to components. The application will ask you to name the template, so that you will be able to search it later on (within the Room component window) using the search field at the top. As you already know, you can double click over it in order to create a new project starting from that shape template.
Note that a room template contains the room floor and walls only; it will not include the covering materials and/or 3D Objects (Furnishings) eventually available inside the original project.
This article is valid for DomuS3D® 2017 and later versions