I use the drink containers has little green houses by cutting the bottle in such a way that the top of the bottle fits over the bottom half. You just have to cut the bottle just where it starts to narrow a bit making sure the top fits over the bottom. Sometimes the second cut is needed to fine-tune the fit.

Here's a picture of some burgundy pansies that I started in the mini Greenhouse. I left the cap on until the seeds sprouted then switched to cling wrap with a few holes for air but not enough for it to dry out.

Great idea Meri

Nice idea, although I've had trouble getting plants out of containers with ridges. Maybe if I didn't wait until they were potbound...