Here is my hightunnel build
http://www.tomatoville.com/showthread.php?t=39087
Get a $75 jig and bend your own hoops, you'll save thousands.
Look up HOA and city bldg permit info. My thread has tons of info about that.
Def. go for double poly. You dont need an inflation blower. I used spacer blocks between the layers, they work great.
Im finishing a 100 ft run of conduit...electric and 1/2" gas line. The cold spring almost got my toms. That wont happen now. So, think about heat now, you'll likely want to add it later.