Depends on how many GPU's you have and how much heat they create.
If you only have 1 GPU then there is no need to build a frame. If you have 2 GPU then you may be able to run them in a pc case if you have a case with good cooling and enough space to fit 2 GPU's.

Any more than 2 and you will need to build or buy a mining rig frame as you usually cant physically fit more than 2 GPU to motherboard without using PCI-E risers. Also more than 2 cards would get too hot in a pc case.
If buying a rig frame, do not buy an enclosed case. Always go for an open frame.
I did an article on steemit a few year ago on how to build a frame..It uses the old style risers so may need modding for new risers.. read comments under article....
https://steemit.com/mining/@pcste/how-to-build-your-own-gpu-mining-rig-frame-stackable-option-for-farms
I may do an updated article soon.