Laptops are kind of more convenient though since i could carry it around
I understand and you are absolutely right - for some, the laptop is the only way to go. I say go for it - as long as you understand and are willing to accept that laptops cost more to purchase, maintain, and upgrade; upgrade options are limited (if possible at all); heat control - especially when gaming - is more difficult; and laptops are much more vulnerable to being stolen (and dropped).
By the way, would it be better if i find someone to build my laptop or just buy one from Alienware
The home/self-built laptop industry is not established - yet. This is because the competition to build the lightest and thinest laptop/notebook has resulted in laptops being very proprietary - that is, parts are made by and for the laptop by the laptop maker. You cannot go into the typical computer store and pick out a case, keyboard, monitor, harddrive, etc. and assemble them into a laptop, like you can a desktop. There is a very small home-build laptop following but parts are still hard to find, and choices/options are
very limited - so the self-built laptop is still in the uber-geek realm.
Therefore, you will have to buy from a laptop/notebook maker, such as Dell (who owns Alienware), Toshiba, Sony, ASUS, HP (who owns Compaq), Lenova (who bought the IBM notebook division) or another established maker.
However, I must warn you again, regardless what the laptop makers tell you, laptops/notebooks are
NOT gaming machines. The laptop is suited for business travelers and other folks constantly on the move, such as students. Heat is the big issue - 3D animated gaming is one of, if not the most demanding task you can ask of the CPU, RAM, hard drives, power supplies/regulators and graphics systems in
any computer. Gaming results in extreme heat control issues for
any computer and the very nature of laptops/notebooks - that is, a powerful computer in a small enclosed space - makes
serious gaming on a laptop impractical. Period.
See:
Gaming laptops are a complete joke - a bit "tongue-in-cheek" but still applicable, and true.