your all saying it, but why not

it sounds like a great job i love building and doing it for a job would be amazing
Get this idea out of your head right now. I had this stupid moment in my life where I wanted to build bloody car audio systems, when I was thinking of what do to after year 11. What a silly thought that was, and good that I look back at it and that I didn't take it anywhere. I also thought of building computers too.
Best thing I did was stay in 6th form. Frankly 2 great years where you will build more solid relationships with your peers than you ever have before and just get your A levels, at which point you can then leave with some form of decent qualification to get yourself a much better paying job, or go study at university to get a degree in something specific you find yourself being interested in.
People here build and own nice computers here because they have worked / studied hard and managed to get well paying jobs.You gotta realise here, you'll spend THE REST OF YOUR LIFE building bloody computers. How do you know where the technology will be in 5 or 10 years time? They have god knows how many factories in China where they build prebuilt systems they sell in Currys and the like, and frankly thats what I'd say the majority of computer users buy. It's just factory style work, and you'll be making sod all money from it.
Stay in 6th form and pick the lessons you feel you will enjoy and do well in, and really think about what you want to do with your life. Nothing to say you couldn't perhaps build and sell computers in your spare time for enjoyment, but trust me don't do it as a career.
I have a friend who after 6th form wanted to skip uni and set up a computer building company. I think he made 1 computer and lost money on it, then ended up going to Uni a year later than the rest of us.