I also think its a great idea, and I it could be used not only for homemade pieces, but also as a resource for growers. Along with homemade bongs, people could post about how they converted their cabs/pc cases, or whatever do-it-yourself jobs they made that are related to ganja.
Yes it would be very useful to show others that wish to build any homemade device from Bongs to Hydro set ups and so on. This would also free space in the other forums where these type of threads are usually posted and make finding DIY projects a much easier task. I think A DIY forum is a very good idea.