Rigging new mast

[glynn]

This is a bit of a big question, but..

I am just completing a 35ft cutter and am hoping to do all the rigging. I have the hide and the marline for the soft eyes and am ready to start, but when these are made how can I possibly get the length of these until the mast is stepped, and then how do I bring it all together.
I know the plans will give me a rough idea, but there is no guarantee my home build will come out as per plan.
Brion's book talks of rigging a mast, but not from scratch.
Any suggestions wwould be appreciated.