Here is a piccy of my homemade polytunnel taken when building the raised beds. the sides are straight up to 5ft then curve. this allows full use of the width as no room is lost where the tunnel curves. The pipe is slid over 8ft lengths of scaffold pipe knocked in 3ft.

I have added a 20mm conduit strenghener through the very top of the pipe to stiffen things up just like on a bought polytunnel. The structure is immensely strong and has cost just £95 for the cover with the rest salvage.