What to use for sculpting?

Hello All,

I'm new to this whole conversion / modelling side of the hobby, and I've had this hankering to try sculpting a Tyranid Swarmlord but one that looks like a giant Genestealer.

I know this is a hefty project to throw myself into, but hey, go big or go home.

My question to you professionals is what kind of clay / tools / framing should I use to do this project of mine? I know green stuff alone won't be good enough to do a big model out of, but I can use for detailing. I was also thinking about constructing a body frame for the model with thin metal rods or something, just to give it a base to build off of.

Again, I'm completely new to this, so any advice would be appriciated .