after a long time fiddling with it I'm kinda proud to present my spreadsheet which calculates the fabric pattern of dome tents. It is based on the poles being parabolas which works pretty well for tents in the "usual" sizes.
The spreadsheet is in .ods format and can be opened with open office.
You enter your basic tent measurements in the upper left hand corner.
You will then get two sets of coordinates(X1/Y1 and X2/Y2). These represent the fabric patterns along the width and the length of the tent. The zero/zero is at the apex of the tent.
Hope someone has any use for it,