Prior to 2003, 100 worked in a number of different places. For quite awhile, we have had a room that was maybe 7'x15' that we stored all our stuff in. It was impossible to work in it, as it was packed, which mainly meant doing any kind of work outside in the hall.
In 2001, and a few years prior, we worked in a shop a parent had at his house. It was a great place to build a robot, but pretty far away from the school, which was a little limiting.
In 2002, we worked almost exclusively in a machine shop at the Stanford Linear Accelerator. It was a great place to work, because we had every tool imagineable, tons of space that was relatively unused by others, and materials/other random stuff a FIRST team might need. It was relatively close to the school, which wasn't really an issue. The greatest part about working here was that we didn't need a teacher with us everytime we wanted to meet (which would have been the case had we been at school). This led to being able to hold much longer meetings, more often, which seemed to be much more efficient. It allowed things to be much more fully completed, in a single period of time.
In 2003 we moved back to the school for a number of reasons. This year was also unique because students from another school in our district joined our team. We also got a second room that had been used as a science office. It was a decent size, and combined with the original room, usable for our purposes. Whenever we held extended work sessions we also used some of the science rooms for the extra space.
The one real disadvantage that I found to working at school where we had only the barest essentials of power tools was that if you couldn't cut it with a hacksaw, or use a hand drill/drill press, it had to be saved and taken up to be done at the shop at SLAC. It wasted a good amount of time, whereas in the previous year, if we needed to mill a slot, or pocket, or whatever, we'd walk over and be done with it in a short amount of time.
The other limiting factor was needing a teacher present at all times, both to unlock rooms, and for legal reasons. We had a few dedicated science teachers who were great, but nobody could expect them to be there 24/7.
I'd say overall, your best bet would be to try and find some kind of dedicated space that is large enough for you to effectively work, and yours for the duration of the build period, on campus or not. Once you have your own space, you can start thinking about all the nice machine tools and other toys you'd like to fill it with
