This is a build that I'm planning to buy this summer, however, I'd like some tips or any improvements if possible
PCPartPicker part list / Price breakdown by merchant
Don’t know what price you are getting the GPU at but I would get the 1070 Ti or 1080 instead.
I think that that might depend on what settings and resolution he wants to play at. the 1070 is great for 1080p 144Hz gaming, while the 1080 is better for 1440p 144Hz. the 1070Ti could work like the 1080, especially overclocked.