they're super easy. just cut your sleeves off and then get a pair of pants that are the size you want. lay them over the sleeves and cut to the right length (leave a good inch or so to fold over for the waistband (the amt will depend on the size of elastic you're going to use). I then slide a pin in where the crotch it and cut each sleeve to that point. turn one inside out and match up the edges and stitch them together (i do extra stitches at the crotch and then go back and either do a zigzag over the edges with my reg maching or use my serger to prevent fraying). then just fold over the waist band and stitch all the way around leaving a small opening to run your elastic though. thread the elastic, stitch it together and stitch the hole closed and that's all there is to it.
Re: Anyone make longies from old sweaters
...Baby Blog...CD Blog...
My sewing skills are basic, too! Here's a link to my blog post about making wool longies: https://rookiesewer.blogspot.com/2011/02/wool-longies.html
Mommy to DD1 (June 2007), DS (January 2010), DD2 (July 2012), and The Next One (EDD 3/31/2015)