I've done a few, and it is fairly easy if you are handy. It's upholstering 101.
A second person would help, but not necessary. You only need one yard for a 4x12.
Hardest part is removing the old staples and making it ready.
Paying close attention to alignment of the cloth pattern.
When I do it, I use a straight edge to cut the first side perfectly straight with the frame.
Staples should also go on a diagonal to give it the best grip.
Start on one side (either top or bottom).
Line your straight edge cut with the inside top rail and staple across the whole frame about one inch apart.
Fold the material over the top edge and lay the frame on top of the cloth.
(this is where a second person would help)
Pull as tight as you can in the middle and fold it over the back of the frame.
Place your first set staple there.
Continue to pull and staple from the middle out to each edge, making sure the pattern stays straight.
After the top and bottom are done, trim off the excess material on the bottom with a utility knife and a straight edge.
At this point, you will need to make relief cuts at all 4 corners so the corners don't bunch up. You can cut it parallel to the frame or at a 45.
Then simply pull the material over one side, making sure it is straight to the frame. Pull staple, pull staple and so on.
Repeat on the other side.
Then trim off all excess material and you are done.
You can get plastic piping and run that around the whole frame for that Marshall cabinet look.
Hope this was helpful.
Good luck.