Building a tee gun is completely pointless. The highest air/water ratio you can get with that is 10:1 or 8:1. Typically this means most people will be running .5-.7 GPM. This will maybe make an inch of snow in an hour is there is absolutely no wind.
Build an Sm4. (The plans are described by someone who posted earlier in this thread) With the same amount of air for a tee gun, you can use more than 6 times the water. Which means ALOT more snow.
I would strongly suggest joining snowguns.com if you want to make one.