These five shapes can be used to connect lengths of standard PVC pipe into a framework to hold tarp or plastic sheeting.  The system is infinitely expandable by adding modular sections of any dimensions desired.

These models are sized for ¾" (i.d.) schedule 40 PVC water pipe commonly available in home improvement stores in the USA.  Since it's an OpenSCAD parametric model, it's easy to change the dimensions to suit your locally available materials.

My wife uses these shelters to cover her vegetable garden during the winter months.  Also makes a great blanket play fort for the kiddos!

Use something between 50% and 80% infill so the shafts are strong enough to withstand the torques applied by the pipes.