I sat in the corner of the room watching them, stoned out of my gourd and filled with happy engineering pride at my creation. Just build an enclosure around it that allows air-flow for the flame, and keeps the 'bowl' high enuf above the flame so that you don't begin burning the pot. Would some Mech. Powdering the pot helps, but in the process, breaks the resin glands on the leaves, accelerating the oxidative degredation of the cannabinoids. Because Most homebuilt vaporizers are a pain to use when you're high.
Vaporizers are less portable and concealable than pipes.
I believe that vaporizers are a tremendous business opportunity, and that they will explode in popularity as soon as they are commercially available. Designing vaporizers is a lot of fun. It's a great exercise in dealing with basic design problems, and solving them with whatever materials are available. I'm working on my third device now, and if it works well, I will 'publish' plans. As for now, here are some tips you might find helpful in your quest.