I say this every time I see this kind of thread, just kind of as a warning...
I had a pen set up in my bedroom for Luma when we brought her home. Within two weeks of having her she had learned to climb over the pen and escape. If you buy a pen from Petsmart they will let you exchange it, even if you don't have the receipt and it's been out of the box! That was excellent, because we switched it for a crate and she learned how to open that as well.
gotta watch the little ones! They can be very sneaky and get into all sorts of trouble...so just be warned ex-pens are not foolproof and you should make sure to "puppyproof" the house.