I just used a cheap piece of 15x20 6mil plastic from the farm store ... I was hoping to get enough for two off one sheet but it was just a little too short... I used the 10ft pvc. The greenhouse plastics will last much longer, you probably won't get much more than a year from the cheap plastic but other than that it works fine.
I pretty much did mine the way this guy did his...
I wouldn't even attempt to heat mine, it doesn't hold heat real well at night, from what I understand if you're in a zone 5, a hoophouse is like a zone 6... I'm guessing it's maybe 5 degrees warmer at night. They do heat up fast though with some sun on them.