Simple title, not so simple task.

I'm interested in making battlemaps solely for the use while DMing my Pathfinder games via the virtual tabletop Roll20 (Roll20: Web-based online virtual tabletop for all roleplaying games (RPGs)) I'm interested in making them as detailed as possible while maintaining proper structure and level design.

Basically I'm just looking for advice on where to start and the best methods of building my own environments and dungeons. I would be interested in creating 3D elements and using those in my maps to create the old school faux 3D that I grew up with.

Thanks in advanced for any help and advice given, I look forward to being a part of this community and posting my results.