you need a computer and some rolls of filament.
That's it really.

To find specs - just do what you would do to find specs for anything else: use a search engine.

To make your own stuff - the best bit in my opinion.
You will also need a cad program that you understand and that is capable of outputting solid models in .stl or .amf format.

Couple good places to start:
http://www.123dapp.com/
http://www.openscad.org/

there are many others - again, just search.

Also lots and lots of videos on youtbe, I quite like angus at makers muse.
Seems like an honest guy, plenty of enthusiasm: https://www.youtube.com/user/TheMakersMuse
And he does get some very nice toys to lay with :-)