Yup been there done that.
Made the first one out of a load of treated pine I had with benches made out of decking timber. Wasnt portable as I needed to anchor it into concrete because of wind....you will need to do the same.
Covered it in that greenhouse plastic treated for UV. First year plastic ripped. Looked into buying either glass or polycarbonate...price of doing it in both was crazy. Glass isnt as good as it lets out a lot of the heat during the night whereas the plastic sheet and polycarbonate keeps things more toasty.
Do yourself a favour and do what I did in the end and that was to buy a Palram boxed kit. For the same price or less than buying the polycarbonate sheets you can buy a whole polycarbonate greenhouse kit.
They are a bit tricky to construct.....do it in a garage if you have headroom, then lift it out. You wont need a tractor....they are really light, two people could lift it easy.
I bolted on brackets then concreted. You could do the same then just unbolt when you want to move it then bolt it on to the other pre-made buried blocks and brackets.
Here's one:
Amazon.com : Palram Nature Series Hybrid Hobby Greenhouse - 6 x 8 x 7 Silver : Patio, Lawn & Garden
Here's the full range:
Greenhouses Archive - Palram Applications
Get the optional window opener. It has oil in a piston which moves when it reaches 70f.
It closes again at night by itself.
Amazon.com : Auto Vent Kit for all Palram Greenhouses : Greenhouses : Patio, Lawn & Garden
If you go this route, make sure you get one with a base like this, some of them don't, they just have an aluminium rail at the bottom.
This one was galvanised but I painted it for a bit more protection as the steel is thin (the rest of it is aluminium).
I bolted through the 4 corners where the pieces join. The bracket is L shaped.
View attachment 451472
Mine is a 6x8 Harmony, all clear panels, which is quite a good size. Instead of the expensive greenhouse staging you can buy I used some storage shelving I had spare (which is cheap to buy) and replaced the MDF shelves that comes with it (MDF tends to fall to pieces when it gets wet I believe), with the decking timber I had from the old greenhouse.
The sprinkler system has a battery controlled valve timer plus each sprinkler can be turned off individually when not needed.
So with the self opening/closing vent and the automated watering system, the whole thing is almost set and forget.
The greenhouse is almost two years old and still looks like new and has been in some high winds and the polycarbonate doesn't show any signs of aging.
The only issue I have had with it is that it can get too hot in there.
