I've never come across a good source of free information on guitar building. I've just learned the hard way with a little wood working knowledge, theory, and common sense...for electrics, anyway. You might just want to start with a public library and see what books they have. It's hard to buy them because most book stores don't carry books on guitar construction and on the internet it's hard to tell what you're getting before you buy it. If you need any tips on making electrics I'll give you whatever advice/help that I can. I just don't have the shop space to attempt an acoustic yet so I can't offer much help there.