Cut your 10ft length of pipe into sections.
2 x 19cm - lower sides of frame
2 x 24cm - upper sides of frame
6 x 36cm - middle sides of frame and cross pieces of frame
It's not as important to use these exact lengths as it is to make sure the pairs are exactly
the same. Otherwise the frame will be lopsided, and feel funny on your back.
Now take four of the six 36cm lengths, and bend them to your desired angle. I bent mine with a 5 gallon bucket, but you can use whatever round object you may have.
eHow had a great explanation of how to bend PVC, so I'll include the link to their instructions. http://www.ehow.com/how_4796089_bend-pvc-pipe.html
My bent lengths are now about 33cm on a straight line from end to end.