My main base material of choice for any of the scratch-built props I've made over the last eight years (TNG Medkit, TNG Dermal Regenerator, Custom Commbadges, Custom Phaser, etc.) has always been sheet styrene. I find it a very versatile medium and suits my purposes rather adequately.
In fact, the Mk VI helmet I'm currently working on is comprised of sheet styrene layered over a basic HALO 2 Pep file. A lot of work's gone into it so far in terms of applying the couple layers of styrene, as well as working all of the surface details in by hand (the HALO 2 .pdo's are low-def).
Like timonemycat mentioned, it's a nice strong material to use (also very light compared to fiberglass, even built up/layered), bends nicely and is easy to cement together. The biggest thing you'll have to worry about is filling in any gaps between the pieces, but compared to other materials requires very little sanding to get a clean, smooth look to it.
Take a look at my WiP thread linked in my sig below to give you an idea of what I'm talking about.
Btw, just out of curiosity, what exactly is going to be
your process for building this up? Are you going to go with a similar approach (layered styrene outer frame over a printed Pep file)? Or do you have something else in mind?
