If you're going to be scratchbuilding, you'll need several thicknesses of both sheet and strip styrene on hand. Evergreen also makes rod, tubing and angle stock. Plastruct also makes all kinds of structural stock, but one caution: If I recall correctly (someone please correct me if I'm wrong), Plastruct can't be glued with ordinary model glues; you have to use super glue. All that stuff will be available at any good hobby shop or model railroad shop; often in their own little kiosks. One more thing: Get a clean small container of some sort (a baby food jar is ideal). As you make your own parts, you'll inevitably have small to tiny bits and pieces of leftover plastic. DON'T THROW THEM AWAY, put them in the baby food jar. You'll ultimately find some use for those "dibs and dabs" in a future subject, sometimes without even having to cut them to size or shape!