Back in the late '80s, I wanted to start raising my own seedlings (which are bloody expensive), but couldn't afford a greenhouse/plastic house/glass house, money being somewhat tight at that time (I suppose in that respect nothing much has changed!) I also wanted to get an early start in with tomatoes , capsicums, cabbages, etc.etc. I needed a small plastic house of sorts to raise them in so that they were warm, had plenty of sun and were safe from frost and wind. I had to be able to make it from what I had lying around but also then (same as now) space was at a premium so it had to be able to be folded up when not in use so that it would store easily. It never ceases to amaze me the amount of crap that one accumulates over a lifetime, an interest in self sufficiency tends to feed that tendency and while I am picking up an interest in the voluntary simplicity movement, I think it is going to be difficult to cut back.
I had some lumps of 20mm thick plywood hanging around left over from a stint working with a plywood company so I decided to use them. One piece was 985mm x 485mm so I used that as the base and cut two sides to fit, these being 485mm wide by 385mm high. This proved to be high enough to allow for seedling growth. To keep the apparatus foldable, I used two hinges on each side to attach the ends to the base, but then I needed to keep the ends from folding flat in an unauthorized manner. To do this I took my trusty brace and bit and bored a depression at the top of each of the side pieces, into this depression I fitted a cut off piece of broomstick to keep the two sides apart (No dear, I haven't seen your broom! Why do you ask?). This leaves the front, back and top open.
To provide the required degree of protection I used thick plastic to cover the open sides, attached to the ends by a lath tacked on to the edge. The plastic that I used was industrial shrink wrap, nut any think, clear plastic would. We have a mob that sell greenhouse supplies not too far away and they sometimes have off cuts of greenhouse plastic, if I were building this today, I would probably go for the greenhouse plastic because it will last a number of seasons. Most of the other cheap and readily available plastic such as urea bags, or even stretch wrap, will only last one season, so plan on it being a consumable item. To improve ventilation and provide access to the seedlings, the plastic does not go all the way down at the back but stops about 50-75mm short. I also drilled 6mm holes in the base on a 50mm square to improve ventilation..
On the whole, the beast works well, but it can get too hot as spring progresses, or if an unseasonal hot spell occurs. Water must be kept up to the seedlings. Covering the punnets or flats with a couple of layers of paper keeps the moisture in during germination, or use a cat litter tray full of sand on which the punnets sit to act as a reserve of moisture. Covering part of the clear top with cloth or shade cloth can also reduce heat input.
Now, having seen it work raising seedlings, then be folded up an put away, it occurred to me that it might be useful later on in the year to dry surpluses. I made up a wooden frame and stretched fly screen material (new not used!) across it to ensure all round ventilation. Fresh, juicy capsicum pieces are totally dehydrated in two good days of sun, the same goes for chillies and onion. I have not tried fruit, but it may take longer because the pieces would be larger. As a drier it is not as efficient as some I have seen, and if large amounts of produce are to be dried it would take a bloody long time! However it costs nothing and so is worth a go.
The seedling raiser/food drier was constructed using material I had on hand, and so my design should be taken as a starting point from which you can develop your own ideas. One suggestion for improvement is to cut openings in the wooden sides and screen them off or install hinged doors for better ventilation/access.