I have seen some other ideas on the interwebs for making your own dip/pullup weighted belt...here is my take on it:
Start with 3 feet of flexible PVC (I used 1 1/4" ID), 5-6 feet of chain, and a load-bearing carabiner style spring clip (the one I purchased was good up to 200 lbs. of weight).
All of these items can be purchased at Lowes, Home Depot or any other DIY type of store.
Then assemble like you see below. It's easy and anyone who passed Kindergarten should be able to "build" their own! :)