When I started looking for information about greenhouses early this year, by luck the first book I got was Shane Smith's Greenhouse Gardener's Companion, which turns out to be the "bible" on the topic. There are some other helpful books as well (notably Greenhouses for Homeowners and Gardeners, by John W. Bartok), but one of the suggestions in Smith's book caught my attention because I had had success with it in my garden, and that was the use of raised beds.

So I decided to devote a lot of growing space to a raised bed in a "peninsula" plan, as shown below (1 square = 1'). The pond will have to wait a while, but I've left some space around it for a chair or two, or perhaps a small tree in a half-barrel. The main aisle has to be three feet wide to accomodate a garden cart, even though that decreases growing space. Bench space on either side of the laundry tub will allow for potting & other work. I plan to put in a small water heater under the bench by the sink.

The raised bed is 20" high, and I decided to build it of untreated wood for a couple of reasons: concern about arsenic leaching into the soil from pressure-treated wood; the possibility that I might want to re-design things after a few years' experience; and finally, cost. To prolong the life of the wood, I lined the inside of the raised bed with a continuous double layer of 6-mil plastic, as shown in this section through the raised bed:

And here's how it looks in the rough (the excess plastic will be trimmed off):

For a weed barrier, I put down the kind of protective mat used under rubber pond liners: it's a felt-like, nonwoven fabric that's heavier than most weed barriers sold for gardens. Over that, there's an 8-10" layer of coarse gravel, then about an inch of finer stuff. I want to put something more stable in for the main aisle, to allow for wheeling a cart, but I haven't quite decided what; for the time being, I think I'll use heavy rubber interlocking ring mats, as shown below; these are made from recycled tire rubber and have 1" holes for drainage.