thanks to everybody for your input. i am going to stick with good ol' silnylon (or possibly even DWR nylon, which would work well for a tent like this), mainly because of cost. this tent will take a substantial amount of fabric. i'll revisit spinnaker in a few years when we feel like our kids are ready to be under a tarp (right now, the oldest would just wander off into the woods and get lost).
as far as sharing plans, please don't take this the wrong way but i don't feel right about helping somebody else do a knockoff. if it was my own design i'd happily share, but i feel i'd be on ethical thin ice with somebody else's hard work. that siad, it's not at all difficult to figure out from looking at pictures and doing some very simple math. for conical/pyramid tents, it's all about A squared plus B squared equals C squared.