Reddit reviews GREAT STUFF PRO 14 Dispensing Gun
We found 2 Reddit comments about GREAT STUFF PRO 14 Dispensing Gun. Here are the top ones, ranked by their Reddit score.
The product is easy to useThe product is highly durable and handleThe product is manufactured in China
Just to add to this, don't skimp on the gun because the cheaper ones can break easily and end up being as bad as the one time use cans. I've heard good things about this one: http://www.amazon.com/GREAT-STUFF-PRO-Dispensing-Gun/dp/B0002YOMJE/
And if you don't feel like spending ~$50 on a gun, just buy the "one time use" can and spend the time to clean it the nozzle as has been described in the other comments here.
If you decide to attempt this, get an applicator gun. You can adjust the spray from a tiny bead to a garden house, it has superior control, the cans are larger, and you don't waste an entire can if you don't finish using it that day.
Also, give this article a read. You didn't specify if you needed to insulate the underside of your roof or not.