Upholstering a chair.
The same method works for the sofa.
I used Pellon WonderUnder to attach the fabric to my chair. For those of you who do not know what this is, it's a paper backed adhesive web that turns any fabric into fusible fabric. I bought mine at Walmart for $1.27 a yard and it is about 18" wide.
After making the sofa I decided that it was to deep, so for the chair I took 1/2" off the depth. I think it looks a lot better.
Building a Sofa
I am using 1/8” plywood because I have plenty on hand and this will make a sofa sturdy enough kids to use. Cardboard, foam core or thicker plywood could be substituted with minor adjustments. Several of my parts will be built up to the thickness that I need. I am also making the cushions out of plywood. I use a utility knife to cut my parts. Three or four scores and I’m through it.
I chose a style that has straight lines and looks fairly simple.