Okay, so enough talk. Let's build!
The base is 10' x 5' of 1'' pipe. My PVC came in 10 foot lengths so you can layout the base with just three pieces of pipe and cutting just one 10 foot pipe in half. After the 5' lengths are cut, layout the base on the ground Use elbow fitting at the corners if you want and get a feel for the size of your new greenhouse. Visualize the amount of space it will take up and whether you plants will fit. Its pretty big using my dimension so I hope you like it. (Building is half the fun so you could just make a second one if you need more space :)
Cutting for the ribs
The 10' lengths of pipe need to be fitted every two feet with a 1" - 3/4" inch T fitting. You need to make 4 cuts in the 10 foot lengths. I wanted the sides to be nice and even. You also want the sides to be even with the ridge beam pipe. (Ridge beam is a term for the center top most beam that wooden rafter attach to in home or barn construction.)
To keep things even, I duct taped the two 1" pipes and the one 3/4" ridge beam pipe together at various point and cut them at the same time I numbered them to keep things in order. (see images)
Reassemble the base with T-fittings
Insert a 1" to 3/4 " T pipe fitting in connecting the 5 pieces of 1" inch pipe and a T fitting on each end. You'll quickly notice that these length need to end in elbows and not T- fittings if the base is ever to reform as a square. I simple cut 1" of pipe off each end and used it as a connector between the elbows and the T. So what you end up with is E-T-T-T-T-T-T-E for each long side where E=elbow and T=T.
The short sides of the base
Take the two shorter 5 foot lengths of 1" pipe and tape them together. Cut 1 foot off of each end.
Connect each piece with 1" T. You can connect these lengths to the elbows on the 10 foot lengths and you base is loosely fitted together but basically complete.
Ignore the Ridge Beam pole in the middle. I'll cover that next.