You will need to check with the school district, but I believe you need to be physically living in the property that you claim to be your residence. Moreover, you will need to provide a utility bill and property tax records. But again, that is something you will have to check with the school district. As far as your building cost question, that can vary. Finding a builder and constructing an actual structure is probably not that expensive - i.e. $250/SF for something middle of the road. However, your real costs are incurred when dealing with the City. When building your own home, you will have to get plans drawn up and submit them to the city for approval. They will have you present your property to the City's Design Review board, which will then critique and make possible modifications to your plan. You will have to pay your architect each time the city makes modifications/recommendations, and you will have to pay the city fees to go through this process. You will also encumber the local neighbors who may not be too open to the idea of you building a 2000SF home next to their single story rancher. I have represented a few builders in the area, and I have seen this process take a few years before they get final city approval and the costs add up quickly. Also, I am not sure what the going rates are for a new water meter, PG&E meter, and sewer, but I can't imagine them being very cheap considering that we are all seeing rate hikes. Well, nope that answers your questions.
If you cannot afford a home currently, it may just be best to rent. The purchase of land is difficult right now due to lending conditions, but it can also be a financial strain unless you intend to build quickly and otherwise take advantage of a finished cost that you could not otherwise obtain in the area. Once you buy land (with financing) it produces no rent, so you carry that loss every month until it's highest and best use is realized.
Best of luck and let me know if I can assist.