The thing that makes a catsuit a catsuit is the way the trousers come all the way to your underarms.
These pages only describe the pattern from ankles to underarms, and don't cover the sleeves or the neckline/closure, so when they mention sewing, you'll need to combine those instructions with the sleeves and neckline/closure instructions.
- Trouser style Most bodysuits are made with one, two, or four bodylength panels with this style for the crotch. Pretty easy.
- Gusset leg This doesn't fit as snugly as the conventional method, because you don't have to muck about with funny curves so much.
- In-set leg If your fabric can't stretch enough for the single-panel bodysuit to work and you don't like the gusset leg, but you really want a seam-free front, try this leotard style.