I love PVC pipe. You can do so much great stuff with it! It's cheap, readily available, easy to work with simple tools, non-toxic as long as you don't burn it, and there are a lot of fittings that make accurate joining of pieces easy. You don't have to be terribly accurate with your cuts and the bed will still come out fine.
This bed was designed and built for my son when he was about 4 years old. The plans have been on my web site for several years and I still get a couple emails per week about them. People always ask me three questions:
1) How much weight can it hold?
Answer: I have loaded my son's bed with >300 lbs on many occasions with no problems. The weight gets divided among the 8 vertical pipes, so each pipe is supporting only about 1/8 of the total load. That statement isn't 100% accurate, but it's close enough.
2) Is it durable?
Answer: My son has been using the bed for 9 years. I think that means it's durable.
3) How much does it cost?
Answer: When I built it I spent about $180 for all the pipe, fittings and glue. I suspect the cost is about the same today.
The bed is made almost entirely from schedule 40 PVC pipe and fittings available from any home improvement store. The design can be easily adapted to a bunk bed. It includes a ladder and railing on the top to prevent your kid from tumbling out at night or when preparing to board a pirate ship. You can make a cloth skirt that turns the bed into a great fort for the kids to hide and play in, or you can put a desk underneath where kids can do homework. At xmas you can hang lights all over it.
I don't recommend this design bed for really little kiddies- they may fit between the rails and fall or go over the top rail if they're getting really crazy. If you're concerned about it you can easily modify the plans to beef up the railing. If you choose to make this bed you assume all responsibility for your kid's safety in using it.
For those who care, the drawing below was made using AutoCAD. You can make similar drawings using Google Sketchup. There is a Sketchup library of schedule 40 pipe fittings here: Sketchup PVC Pipe Library