My primary concern is getting the pole apex at the right height. I am not sure how much allowances to make for venting and silnylon sag. Catenary curves is another variable I am not sure how much to allow for.

Earlier tents have been modeled with cardboard and tape or string and sticks - pretty crude affairs. Now I have the precision of Sketchup and can tweak down to a millimeter. Perhaps a blessing - and a curse??