With your computer case it is mainly cosmetic. You do not need to go all out with it, but you can. It is what you will be seeing everyday. It is your statement, this is your time to shine. In many cases quite literally. Sorry about the bad pun. But you can get a case that focuses on air flow, servers, lighting as in led strips on the fans and inside the case, small cases, big ones, and ones that look like they would fit under a tv for part of a media center. Pick the one that you like, and it usually should do, there is not that much in choosing your case.
But do keep in mind, it has to be able to fit in your motherboard, which has almost all of your components on it. As well as any HDDs, SSDs, Video Cards and any other add on cards. If these fit into the case then you are good to go.
Also keep in mind that your motherboard has a size atx, matx etc. Make sure that your case is capable of holding your motherboard!
Remember to be happy with your choice, as this is the part of the computer that is exposed. Since you will be looking at it day to day.