You can purchase from a dollar store a relatively cheap dome. Pick up a clear plastic storage container and lid. flip it over and put four 1/4 inch holes in the bottom of container. Now you are set up. Buy some clear plastic kegger cups, the small ones. Get yourself an empty egg carton and some paper towels, plain no fancy paterns and ink. Use this to germ your seeds. Make a little nest with a swatch of towels, wet them and place a seed in each pocket, cover over with damp paper towel, shut lid put in warm dark spot. Check every day or two and throw away the rejects after a week of no result. Use your party cups fill them halfway to two thirds loose soil mix, plant one germ per cup head down,seed husk if possible intact, do this when initial root or "radicle" is three times the legnth of the seed itself . "remember head down". This makes the seedling turn all the way around and in doing so it shuks it own seed hull. The plants don't streatch as much initially, and they start much more vivatiosly. Now, that you have done this, you can deal with a little stretch by just adding some soil to the cup around the stem just like pulling up its britches! You are able to control it because you only filled those cups 2/3 full. Use the lid of your dome as the tray portion set your germ/clone warming pad in and then cover this with perolite, at least as deep as the lid. I nestle my cloneing cubes into the perolite set the storage container over it, now with the dome set up I slide it under my four foot strip lamp fixture, this shines through the dome. I've never used it for seedlings, It really isn't advisable. If it is a seedling it has roots and doesn't need to get it's moisture from condinsation formed on the leaves. This is how a clone gets it's moisture while roots form. If you do this to rooted plants, such as seedlings, you will in fact drown your babies. Necrosis will cause the leaf structure to start breaking down resuting in yellow tipped leaves.
