Annetitch, it can be done either way. Mostly, you will want to do which ever is easier, and there are advantages to both ways. If you finish your walls first, you can put in a floor then baseboard and not have to protect your new floor from damage during construction. If you finish the floors first, you will have to protect them with plastic or rosin paper, but you can then do some very interesting details for where the drywall meets your flooring and possibly eliminate baseboard all together.
Your first step would be to pick out finishes (mostly, what type of floor do you want to put in), and generally how you want it to look like in the end, and that should prescribe an order of operations.