Simon just asked me about the polypipe we used to make our frames for net over veg gardens and fruit trees.
Here are pictures of another structure we made using the polypipes and star pickets.

It is a fenced area to display plants for my roadside plant stall. Keeps thieves and deer off the plants.
I saw the idea in an old grassroots mag. It has many uses, such as a vine covered cool place to sit in summer. Put the bbq in it.
Put chooks in it or an aquaponics system.
You could cover the top with net or with a more solid stuff.

The only down side or error we made was cutting the pipes too long, we cut some at 8m long but they bowed down in the warm weather and were unsightly and useless.
So we experimented and found that 4m lengths over star pickets spread at 2.1 to 2.3m apart was perfect.
The taller the star picket the higher the structure, still need dwarf fruit trees if using them in a line. Also bolting them to the picket keeps them from slipping down and being shorter but you can work that out for your self. Am happy to answer any questions.