Before you start. Decide how much you wish to spend on the project, how you want it to look and find out what parts are available for you to use. Some links to help you on your way.

Bryan and associates
Crooked barn
Cooper-T
MaxZBulk
Mac1
Quackenbush airguns

And a bunch of links in case you were not yet confused enough.
Airgun links


Choose a tank there are many.



Tank bulk offers a way to bulk and have hundreds of shots between fills. The number of shots you will get depend on the tank you use as well as the tune of your gun. Here are some pics of different tank bulk options that I have done.