While the image to the right has the wires and middle pole up before the plastic sheeting is added, that'll never happen, as the fishing wire and sheeting is easier to put on before it is raised into place, but it's shown to show how the internal structure is made.
Also centre pole is around a piece of vertical rebar, to hold the base of the pole from sliding around.

The support wires are also inside thin plastic tube, so the plastic sheeting has something at the edges to be connected to. Also the fishing wire is also threaded through holes in these tubes.
The fishing wire is needed to give the plastic sheeting support, as 20’ is too far to reasonably be supported if the wind blows a little hard.

The door is made through one of the surfaces of the pyramid has its own separate extra tube/wire, and can be held open by moving that pole to the other side, and also closed.