Plastic plumbing pipe is the way to go since it is strong and light-weight.
The legs fit into Ts inserted into the top cross bar and by not gluing those Ts, (it sticks together well enough without being glued) you can rotate the legs at the top so you can pick your tilt angle.
You can shim the bottom cross bar ends and the legs' feet for uneven ground. You can have big castors on the ends of the bottom cross bar so you can lift it up a bit by the top and twirl it towards the sun whenever you go by.
You want it tilted higher earlier and later in the day when pointed at the (lower then )sun, so you can have the feet farther in then and set the legs farther out for mid-day to a lower tilt angle. Max AHs! :)