I would spend the extra $40 and get 16gb of ram because these days you kinda need it if you are going to be playing any demanding game.
I would also recommend not spending a lot on an expensive SSD. Cheap Dell SSD work done no need to get something crazy.
Don’t cheap out on the case. Get something that has a lot of airflow.
Don’t get anything that isn’t on par with the lowest i7.
Graphic cards are probably at a good time to buy. I would go with a 1070. I have seen some reviews and will have to get a refresher but I am pretty sure that it is not worth to get the ti or any other versions unless it is obviously much better. Don’t spend money on the TI or “gaming” versions of cards because many are just over clocked or barley give any extra performance.
If someone builds it for you, make sure they download the OS on the SSD and keep all your games on the SSD too.
I had the mistake of having my custom laptop made for me, and they installed the OS on my HHD, which took up a load of space and forced me to separate my games and programs, having some in SSD and some in HDD.