There are many ways to make an effective rooting chamber (or miniature greenhouse, as we like to think of ours), and none of them are expensive. The size and shape depends on the size of your plantlet. Basic plastic storage boxes are great for larger cuttings, while smaller plastic fruit and salad boxes make brilliant mini-propagation units for growing seedlings. A clear plastic bag propped up with a rigid support like a short length of cane makes a simple cover and fits nicely over a standard plant pot. Drainage holes are necessary, allow you to water from below. Shop-bought propagation units will also do the job.
Clockwise, from top: orchid cactus; laid-flat echeveria; jade plant cuttings left to callous