New Computer for designing and gaming

Hello All,

I am planning to buy a new computer for design and gaming. Currently, I am using a laptop.Specs Intel I3 3rd generation, 1TB hard disk, two gb graphic cards.
Using it for the past four years, and now it is outdated.

So I am thinking of buying an intel i7 processor, 256 SDD hard disk, NVIDIA (I didn't decide on the model yet). Should I customize it, or I buy it from the shelf of Walmartone?
What will be better? My uncle works at Walmart, so they get some employee discounts.
Anything else should I consider before buying, I am 19 years, and I am earning enough to cover my laptop/desktop expense.

Your suggestions are welcome.