I built a couch in my living room, without any major power tools! I only needed a hand once, to flip the couch over, lol. I did it, so you can too. You can find answers about dimensions and materials below.

Music by Mittensさん
   / @mittenssan  

Dimensions
Foam: same as a twin bed minus 2 inches to the width (0:08).
Plywood: 12 inches smaller than the foam on each side to spare my shins.

Cost breakdown... the goal was not to be cheap, it was to build a quality couch myself!
Plywood $50 (Home Depot)
Foam $0 (the gym I work at replaced their floors and I snagged some of the leftover NEW foam, with permission)
Memory foam mattress topper $40 (Amazon)
Fabric $110 (Hobby Lobby)
Legs $108 (Amazon)
Feather pillows $40 (IKEA)
Total cost: $348

Other tools
Staple gun
Sewing machine
Power drill
Sharp knife