You just got to look around the house. Eventually when you find something to use, you come up with a design.
being creative with what you can use around the place ( and buy a proper stem and bowl / cone peice )
Pen tube for the downstem, socket for the bowl, cut off the top of a ipod headphone and use the thing as a screen, use a bottle as the bong.
You dont even need to buy a proper stem/bowl. on my ghetto bong I made both of em. Check it outttttt the actual bong is the first pic, the second pic is the Bowl/diffuser, i used steel pipe for the downstem
Milk bottle, Cut the handle near top, done Use the longer part of handle as bowl and stem, shorter part as carb and mouthpiece as mouthpiece. If you dont understand i can get a picture or something