I started to do what you're talking about because I saw a guy building his 'dream' house as features in a single model. He even added furniture as features and the part just kept growing. It was cute, but you'd never be able to figure out how to make something from the way he was doing it.
I was sure that the productivity features built into Pro/e would facilitate architectural uses. So, I began to do it by making some libraries of commonly used materials, like different sizes of lumber. Different instances were different lengths. Another productivity feature is the ability to construct stuff in assembly out of other assemblies. So you could frame each wall separately, making it out of your library studs. Another assembly productivity feature that came in handy was patterning. Standard US 16" centers is conducive to it. If you know how to build it in reality, your building in Pro/e should mirror how you'd do it in reality. The obvious advantage of doing it this way is parametrics. You then create a BOM which tells you how many board feet of certain types of lumber you'll need. It could even tell you how many of what mill sizes by standard length.
For the symbols, you could dxf or iges out the drawing sheets and import them into an architectural cad package.
David Janes