You create a Mass family file. In the creation of the file you have good control over the solids you are drawing and the file I drew ended up looking like this:
A bit grey and bland.
Then you open a new project and bring in this family. Then it is just a matter of choosing the Massing & Site tab and picking on say Roof and picking what you want to be a roof etc.
Then it ends up looking like this:
Of course at some stage in a perspective view like this you have to hide in the view the mass, otherwise it shows through as a grey shape under everything. This building shown has been moved on from this stage - it seems architecture might be an iterative process after all?