I would go buy the feeder, waterer and the chick starter from the place you bought your chicks. A big cardboard box is a start for a home, you need to read about their heat requirements too.
While you are at the feed store, look at any chicken coop building books they have and see what looks like it will fit your skills/time/budget.
You probably have few weeks (and a few new and bigger boxes) before you need a coop. You are probably better off building your own, remember you need to take in consideration your weather and space. If in doubt, you need more space than you think. If you are looking at a cheap prebuilt coop, chances are they are pushing the minimum of space needed and stating the max number of chickens if you bought bantams.
Good luck! And have fun!
I already bought the chick starter, a heat bulb, shavings, little feeder/water containers when I bought the chicks. The have a nice cage that they are in right now.
I know I have four weeks until they need to be in something bigger. I bought 2 buff and 2 speckled sussex chicks.
