I've made pull-ups by sewing elastic around the top of prefolds. Start at the top of one end where the colorful stitching is and pull the elastic as you sew across with a zig-zag. When you get across the top, put the other colorfully stitched edge right flush with the other edge and keep going until you have an elasticized waist. My dd only wears them at night, but she can get them on and then pull a whisper pant on over for waterproofness. I've made one pair of cute ones by folding the prefold in half so that the blue stitched ends are lined up. Then I sew a couple inches down each side. I cut leg holes and put in elastic and serged the edge. Then I sewed elastic around the top. I put a ribbon rose on it, so she loves it. It's her "pretty pull-up".
I also made some pocket pull-ups using some Wraps I had cut out years ago. I found out the PUL I bought was a piece of crap, so I never sewed up the larger sized wraps I had cut out. I got some $1 a yard fleece and terry so I thought I'd give it a try. It worked if I just cut the flaps off of the wrap and sewed the sides together and put elastic around the top and in the legs. I stuff them with 2 washcloths. Like I said, the PUL is crappy, but for her occasional nighttime accidents, it works fine.