Aright, so i been making bongs and pipes outta house hold things as a hobby for about 1.5 years. Its REALLY easy once you get your own pattern down (like style/preference).
If its glass, get gormets and alot of screens. This will make the down stem and such air-tight when you drill a hole in the main body. Bong are a simple and lovely piece of work. Its comprised of 3 main parts.
Body-Chamber, Tube/mouth peice
Downstem- Diffused or not, glass or metal
Bowls- I catagorise ash catchers here too
What you should do is just buy a set of bowls/ stems from a local head shop those work the best (obv). But if ur low on loot and need a downstem/bowl u can use those lil doorstoppers. Their airtight and already formed into tht shape. You dont really need an ash-catcher to make it function properly OR a diffused down-stem but its better to have them.