Have a look at the 'stickies' in the Modders section here
+1 for StealthVape, fantastic....
Loads of links to site for stuff and a couple of guides too
Got my diy starter kit from leisureliquids. As you can see plenty of venders do them. Have a look about and take your pick. (still 3 days to go before first attempt will be ready. plain raspberry)
A box mod can be as straightforward, or as complex as you want.
On a basic level, a 510 connector, battery holder & wire will do you. Or, you could look into VV & VW mods.
There's a couple of ways to go about this.
DNA20 is quite simple to install - so long as you're comfortable with a soldering iron.
Vamo mod - you can buy a Vamo board from Stealthvape and pop it into your baccy tin.
Build your own circuit - there's a few kits available from Stealthvape & Liberty Flights for this. There's also the awesome evercool circuit. Schematics here: http://www.e-cigarette-forum.com/forum/battery-mods/114901-evercool-variable-voltage-mod.html
By way of inspiration, here's one I made with a friend one Sunday afternoon