Tarp Bottom edge Measurement

So I've got in 7 yards of SilNylon and I'm wanting to leave enough on the ends to make a set of doors that I can move around the tarp to where ever they are needed. So I'm trying to decide on the bottom edge length of my tarp.

I've already decided on 11 foot ridge line and I'm set on a 8-9 foot span, but how much should I leave for the bottom edge? Is 5 feet enough? 6 feet too much? What does your's measure?

P.S. Making a Cat cut hex tarp between the OES Standard & Deluxe.