My studio's chair was kinda old and the seat was flat, so I repaired it and turned it into a tres chic element in my studio. I started taking the pics after dismantling the chair, sorry for the missing pic of the chair before the makeover.
Step 2: Dismantle the chair and clean.
If you want to paint the plastic parts as I did you must deeply clean all the parts, so the paint sticks well to the plastic.
*Ask your cat for help, mine helped supervising all the process
Step 5: Now the cushion
-Remove the staples. I did it just with one side for making it easier.
-Take some stuffing material, I got mine from a crafts&fabric store. (and it's kitty aproved)
-Cut the stuff by the size of the chair
-Fill the cushions and re-staple.
-Get your new fabric and cover the cushion with it. Staple. (sorry, no pic)
Step 6: Assemble
-Get all your parts and put them together again.