It sounds like you are new to all of this...
First thing that is VITAL.. The power supply is critical! I would rather have a 350W Antec than a 450W no-name. There are only a handfull of power supply manufacturers that are good. My personal favorite is Antec.
As far as cases, as long as everything fits and there is enough airflow, your choice of case is all a matter of preference. But, in general you have three options.
1) Case with a good power supply.
2) Case with no power supply.
3) Case with a power supply that you will throw away.
Option 1 is probably the best as far as cost goes. Many options exist in the $60 to $100 range.
Option 2 will be what you will do if you opt for a high-end aluminum windowed case, but the total for case+PS will likely be in the neighborhood of $160 or more.
3) Option 3 is a little bit of a waste of money, because you are paying for a junky power supply which will wind up in the trash. But this gives you the most choices.
Also, tell us what you want in a case?? Do you want windows? Does weight matter (will you be carrying it)? How many drives do you intend to mount? Do you need a locking door over the drives/buttons (I have small children, so I do)? Can you afford aluminum? Do you like colors?
In the end, the choice of a case is a VERY personal decision. What is best for me might be the worst for you.