If you're going to pick up a flat pack this is what you should need assemble them:
- 3/4" pipe clamps from harbor freight ($9)
- various lengths of 3/4" (black) pipe from HD/Lowes
- Kreg pocket hole system (~$40 for the R3 on Amazon)
- PL premium ($5)
- box of 1 1/4" pocket hole screws ($15 for 500 on Amazon)
- box of polyfill from Joann Fabrics (~$10 if you use 40% off coupon)
The reason for the Kreg is that you can use fewer clamps for assembly and the screws and holes will be internal, which means you don't have to fill the holes for finishing.
Now if you change your mind and want to go the DIY route then do as Jay1 suggest and grab those tools in addition to the list above. Also you can have HD/Lowes cut your sheets down to size, although I would suggest leaving at least a 1/4" of waste between panels because their panel saw and/or operator tend not to be exact. Alternative is use a circular saw, straight edge with c-clamps to cut to size. A router with a flush cut and round over bit will come in handy too. One more thing to consider is checking your local Craigslist for used tools, which you can use for your projects and then turn around sell once done.