I built my last desktop with parts from Best Buy (except the SSDs which I was carrying over to the new one). They don't have a huge selection so you won't be able to build anything very high or low end but it was very competitively priced and I was able to get it all same day pickup. Their case selection is pretty much limited to the glass side panel/RGB LED stuff though.

This was in very early 2020 just right before everything got crazy so I'm not sure how it is now.