Marshmallow shooter kits with all PVC pieces pre-cut are available in the Instructables store!
This project appears in print as part of Best of Instructables Volume 1.
Instructions are here for the Soda Bottle Safety Goggles.
Step 1: Plans
(22 inches of 1/2 PVC pipe (1/2 is a the nominal diameter, its actual outer diameter is closer to 7/8 inch), 2 end caps, 2 three way junctions, and 2 elbows.)