I used to have a laptop, it was crappy from day one, and as soon as one piece of hardware was broken from poor design, the whole thing was useless. I took it to be repaired and they couldn't because it was welded together... and they wouldn't give me a refund because I had tried to have it fixed >_> sound logic.
Now I didn't directly build mine from scratch myself, however since the local pc store has very little business, they allowed me to stick around for a day and observe them making computers and talking about components and stuff with the staff.
So when I built mine I was stuck to a budget, (We modified a new computer my mum had had built by them because the only real thing it was missing was a graphics card because she had looked up one of their pre made gaming pc's and asked them to remove it, against their advice, to save on costs).
So I have a gaming PC, that had been modified to be a well performing work PC, that we then remodified to make back into a decent gaming PC.
Also I changed to a larger clear perspecs case, to allow the installation of a secondary fan, and a new battery. My mum freaked when I showed her lol.