Consider the price of your time, overheads (heat,light,insurance etc) and wear on your computer. Then determine a per hour rate. Some people I know use an estimate sheet that covers, set up time to create the project files. input time to load or create the model. operator time for texturing, etc. operator time for test renders. machine time for rendering the project (unattended) paper, ink etc if hard copy is required. burning cd or dvd You might charge $50 per hour for complex work charge $10 for machine time overnight. If you can get a 3d file of the building you are way ahead. In my area an architectural firm would charge about $100 per hour for this sort of work.