i'm sinking, oh nos!

okay so have any of you had to fix your own floors?
i mean without the contractor..
okay so the floor in my room is sinking, i have the lowest room, the basement rec room, and i can see the crack in the tiles i have and how theyre breaking because of HOW my room is sinking.
i'm not worried, but it's so annoying to avoid the cracks in order to have my table just right, straight. ugh.
so i want to re-do my room, i sound so handy :)
but the thing is, i don't know how hard it's going to be, and the overall cost..
so if you guys have any idea about this, or have recently done your floors, what do you suggest?
should we hire someone, or do you think i can do this on my own for a fraction of the price with the help of home-depot and a few friends?
do tell!
thankies.
xx