I don't know how to make one, tho ive smoked outta some real good homemade ones. But if u got some cash you could buy a decent one for probably as little as 100$, a good one for 150$, and if u really wanna get extravagant with it, you can buy one of them Volcano vaporizers but that runs ya a few hundred $. But if you smoke tobacco (and chrons) a lot, you should at least get one of the more inexpensive ones and here's why.

Basically, you play around with a temperature control on the vaporizer's heating unit. The trick is to get it to the perfect temperature - one where the THC will be activated but the rest of the chemicals will basically remain intact. In other words, you inhale pure THC, and not the smoke. After a few go's at it, you should have no prob getting the right temp. And you'll love it!!! When I smoke outta mine, I get the chillest, most spaced out high ever.. and it's DEFINITELY much better on your lungs since, as i said, you aint inhalin no actual smoke. u just get the vapor that comes off the THC.