With testingcheatsenabled on, click on the ground of the lot you want to edit, (without going into edit town), while holding down shift. (I think it's shift and not ctrl.) That will give you the option to build/buy on that lot.
To make your singer Sim wealthier, sing for tips as often as you can. If you have a gig, go to the gig site early in the day and just sing for tips all day till the gig, then sing for tips after the gig while you still have an audience.
I started my singer off with one trait that wouldn't be normal for a singer. I made her a klepto. Money problems solved! A quick tour of parking spots each night and she was rolling in dough and had plenty of time to focus on her career. If you don't mind cheating, the testingcheatsenabled trick I mentioned above would also allow you to hammer any vehicle on any lot so you could actually obtain all the cash you need in one day because hammering those vehicles, or art works, puts that cash in your Sims pocket!
