I made a scale model of myself out of plasticine, along with hiking poles and the poncho to work out the dimensions.
Bathtub floor was sewn first, using darts in each corner which were later removed. Grosgrain peg loops were sewn into each dart/corner.
Mesh was sewn onto floor in two pieces.
Zipper sewn directy onto mesh.
Grosgrain loops sewn onto zip fabric for top pulls.
The smallest possible stuff sack was made with the offcuts.