Build a laptop ?

I know it's possible to get the parts and try put it together but I'm not sure if anyone has any experience with putting a laptop together.

Is it worth it, from a cost point of view or would you be better off just buying one.

It's for a family member mainly cpu and ram heavy stuff, was thing the equivalent to a i5 7500 or an i7 if affordable, with 16g of ram. The price point being the stickler, that being aiming for 900 euro.