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Here is a photo of my greenhouse project. I considered this mostly an easy build! Although, I'm moderately experienced with construction in general. I built this entirely by myself, with zero (0) assistance from any other person, so it truly can be done solo. The plans are very simple to follow. I spent just under $500 (USD) with all new material (USA Feb 2015).
The house is built to almost exact original dimension in all respect, with the exception of the door. I installed only one door. I used non-treated lumber, but did use Olympic porch and deck stain & preservative before covering. This wood treatment will last the length of the plastic covering, and we will reapply when we recover in 5 years. We used 1/2 gallon of product. The poly is UV rated greenhouse film (don't skimp here).
A couple of builder's notes: If you build this solo, make sure to the erect the sidewalls and roof on a calm day. Use 8" C-clamps to holds things in place as you screw them down. Think it all through before you tackle each step. I used two ladders to stabilize the sidewalls as I screwed them down to the foundation boards. You will have no problems if you go slow and think it all through.
Once you cover the greenhouse, you need to secure the plastic permanently with wooden "battens." You can do this really cheaply by purchasing a single 4 by 8 foot piece of pressure treated plywood .75 inch thick. You can cut approximately 32 each 1.4 inch wide strips that are 8 foot long. I say 1.4 inch because if you start at 1.5 you end up about 1.4 after the width of the saw-blade eats up part of that 1.5 inch. I recommend you use "lath" screws, as they have an extra wide head that holds the battens down well.
You will notice a steel barrel in my photo. This is actually a water-filled solar heat-sink. Here in Indiana USA, the sun's angle to the earth in Feb, Mar, and April is such that the side of the barrel absorbs lots of light at day, and the heat is released back into the greenhouse at night to smooth out the temperature swings.
During the summer, the sun's angle is much higher above the horizon, and most of the barrel is blocked off from the sun's light by the shelf that is now built over it. The barrel does not absorb very much excess heat in the summer. The barrel weighs 400 pounds filled with water and so we bolted it to the frame of the greenhouse and it makes a wonderful house anchor as well!
This entire project only took me about 30 hours, which included the earth work. I had to haul in 3750 pounds of gravel, about 1000 pounds of dirt, and about 400 pounds of wood chips.
It was a fun project!
Cortland Carrington, Bloomington Indiana, USA