Isaac Clarke, the main character of the Dead Space series, started off from the beginning as an engineer and Dead Space 3 wants to show off his true talents through weapon crafting. In Dead Space 3 the benches used to upgrade weapons in the previous games will now allow you to create your own unique weapons from scratch.
These weapons and blueprints can also be shared with a co-op partner in the game, if you choose. As you go through the game you will pick up pieces and components for weapon building as opposed to simple blueprints of weapons already built. This means you can make a Ripper gun with a flamethrower attachment, a Plasma Cutter with a Tesla coil that shoots electricity, and much more.
Dino Ignacio, UI Lead for Dead Space 3, explains in the below video about how weapon crafting will work in the game. Check it out: