First I decided on what size I needed, this one is 19 feet long by 14 feet wide. For this size I used one inch PVC pipe. I used two ten foot pipes and two 2 1/2 half foot pipes. I connected the ends with tees and the center arches with cross tees. I ran a pipe lengthwise at the top to strengthen and tie the arches together. I also added a pipe vertically to the ends for extra strength. If you are going much smaller then ¾ inch pipe may work for you.
I glued the pipe together and lined it up where I wanted the greenhouse. I then drove a 2 to 3' piece of rebar into the ground at one end of the greenhouse, and next to the pipe I had laid out. The rebar is for the pipe to slide over, this holds the pipe in place and secures the greenhouse to the ground. I then drove another section of rebar next to the other end of the greenhouse and ran a rope to line up the center sections of rebar; driving rebar next to them. Then measured the other side and did the same there. When the rebar was in the ground I started at one end and slid the pipe over it, working my way from side to side to the end of the greenhouse.
I also used a length of rope to tie the arches together making them sturdier.
For plastic covering I went to a farm supply store as they sold plastic sheeting in 20' widths, and I got a 20'x50' roll of 6 mill plastic for $60. The stuff I found in the hardware stores was less expensive but it was 10' wide at 6 mills. Ten foot wide was not what I was after; it could work on a smaller version of this green house.
To pull the plastic sheet over the top of the greenhouse I placed a length of 3/4 " pipe on one end of the plastic sheet to use as a way to pull the plastic up and over the one inch pipe. I taped rope to do this and pulled it up like a sail. I used outdoor duct tape to secure the plastic sheathing. A friend who likes the idea said he was going to try using grummets and tied the plastic sheet down.
On this greenhouse I added a gate and used deer fence to let air flow through and keep out the deer.
