Commercial Scenery and Architectural Details

[Ahistorian]

I plan to start trying to create some buildings in the next month or so, which will hopefully eventually be available for sale. Am I OK to use Wills sheeting on them? What about doorways, windows &c? Is there are a certain amount of detail that can be provided out of my bits box, or must it all be done from scratch?

Any & all help & advice appreciated!