Building you're own stretched canvas is so simple, and SOOOOOO much cheaper than buying a ready made one from the store, especially one this large. the finished dimensions are 48" by 48".
What you need:
Mitre saw (chop saw)
Staple gun and staples
60" of 60" wide canvas (I get mine from Joanns. it is in their duck cloth section and costs $9.99 a yard, use a 50% coupon)
start by cutting 2 of your 2x2's in half, so 48". So you will have 4 48" pieces.
Now you will cut mitered edges so that the wood pieces fit together at a perfect 45 degree angle.
position your chop saw to 45 degrees and cut the edge of each piece of wood, ONLY CUT ONE SIDE OF EACH PIECE OF WOOD
Now position your chop saw to 45 degrees on the other side of the saw and cut the other end of each piece of wood to look like this:
Now take the 3rd 2x2 and mark and cut a piece 45". This will be your support beam.
You are done with your cuts, fit together your pieces to make sure they fit flush.
Time to screw it all together, Take your electric drill and screw the pieces together. you will want use two screws per joint. Position the screws so they don't meet each other and deviate, so screw one on top and one on bottom as shown in the photo:
Go around screwing together all the joints. You'll want to screw the support beam at an angle so that the screw reaches the adjoining 2x2.
You are ready to stretch your canvas! Lay out your canvas and staple one side (I suggest to wrap and staple right underneath the support beam first)
go to the opposite side and pull and stretch until your canvas is pulled tight with no wrinkles and staple.
Do this same method with the 2 opposite sides. until you have a staple on each side of the canvas, pulling it tightly.
Now work your way around the entire canvas pulling and stretching as hard as you can until there are no more wrinkles. wrap the corners like a present.
You are done and ready to paint!!