I've been making hula hoops for about two and a half years. I've tried to include here the wisdom I have gained from making lots of hoops. I use the tools that I've found in my mum's garage, as you may not have the same tools, I've tried to suggest possible alternatives.
Step 1: You will need ....
*MDPE water pipe
This blue tubing comes in 25mm and 20mm diameters. You can get it from DIY stores like Wickes or Screwfix. Unfortunately the smallest length it comes in seems to be 25 metres.
25mm tubing is good for adult hoops. I use 20mm tubing to make lighter hoops for more experienced hoopers, for hand hooping and for children.
This is the part I've had most problems with. You want something that fits snugly into the water pipe, so that the join won't come apart. You also want something strong which won't break. For the 25mm piping I have found that a short piece of 20mm piping makes the best connector, but clearly it isn't worth buying 25m of pipe to make a 10cm long connector.
An alternative is to use "pipe inserts" which are little tubes with a ridge round one end. These are designed to strengthen the pipe at joints and therefore fit very well in the pipe. They are usually available from the same places where the piping is sold. I use these for hoops made with 20mm pipe.
You might also come across something else that can be used as a connector. Fancy Tapes sell barbed connectors, but I haven't tried these. For 25mm piping you need a connector with an outside diameter of around 20mm, for 20mm piping you need a connector with a diameter of around 15mm.
To get the connector into the pipe you usually need to heat the pipe. I use a hot air (paintstripping) gun, but hot water, a fan heater or some other source of heat will probably work just as well.
Sometimes a connector will stay in place just from using heat, but not always. I therefore use glue. Most glues won't work with the polyethylene which the piping is made from. The only glue I have found that does work is Loctite Super Glue All Plastics.
*Pipe cutting device
I use a copper pipe cutter to make a groove in the pipe and then slice through with a stanley knife. I used to use a hacksaw, but this leaves a rough surface at the pipe ends which needs to be filed or sanded down. You can also get a special tool to cut plastic pipes.
For cutting the duct tape.
*rag or cloth
For wiping up glue
*secateurs or file
If you are using a pipe insert as a connector, you will need to either cut or file off the ridge round one end of the pipe insert. I have a pair of secateurs which are good for this.
in case things go a bit wrong
*tapes for decoration
to make the hoop grip better, and of course, look pretty.