I'm not an Alumni Development Director but my recommendation is that you might want to speak with one in your area. My experience has been that the best donors to schools, in general, are alumni.
If you want to find someone who would be "passionate" about a new building, think about someone who went to the school and would like nothing better than to see a new facility for it! The older the school, the better, since you'll have a larger pool to draw upon.
So begin to think about tracking down those who went to the school. Tell them about what you're trying to accomplish and get them excited about it - tell them about what's new at the school and why a new building is important.
Of course, parents can also also key donors. And don't forget teachers and staff - you never know! Anyone tangentially involved with the institution should be part of this new endeavor.
Best of luck!
