The next step is selecting the right case.
Obviously you will want to get a case that looks good. However, the a case you select also need to have plenty of air flow to keep the CPU, motherboard, RAM, hard drive and graphics card(s) cool.
Gaming at maximum settings tends to put these components under load causing them to heat up very quickly. Good cooling will serve to keep all these components humming along nicely.
Good airflow requires plenty of vents and a decent number of fans and usually means a larger case. Also high end graphics cards tend to be quite long and need slightly bigger cases.
So it is necessary to ensure that there is adequate space available to keep the case and provide airflow when you need to use it. You don’t want to end up with a PC that won’t fit where you need to keep it or will not get adequate airflow.
If space is tight, then selecting a smaller case might be necessary. However, this will mean less airflow and possibly having to use a less powerful graphics card. Also if you would like an extreme gaming next day PC in a small case, you have to be prepared for it to be noisy. Since there is room for fewer fans inside the smaller cases, the fans that are installed need to rev faster to provide adequate airflow, which obviously means that they will be noisier.
As mentioned above it is possible to get cases which have some soundproofing features built in to reduce noise levels and if quietness is important, it is a good idea to go for one of these cases.