We haven't written up specific instructions, and unfortunately the photos we THOUGHT we had of the phases of its construction weren't there for us to share. :-(
Our first step was to get the windows; a wide variety of sizes, shapes, and conditions.
Second, we created paper "miniatures" to represent the windows. I used grid paper so that we could count the squares on the grid... for example, if a window was 36 x 24, we cut a piece of grid paper to represent it. To avoid wasting tons of paper, we halved it so that the representative piece was 18 x 12 squares, with each square of the grid paper representing a two-inch square.
We spent several evening laying out the paper pieces to figure out how the windows could possibly fit together for four sides and a slanted roof (our choice of "design"). We finally got a good fit with the windows with minimal gaps and edging. We also decided rather than framing out to the top of the angled roof, we would let the windows end low and then fill in the triangular gaps (visible under the roof edge) with plastic. If you want something more elegant, you might make your windows fit more fully to your roof, and then fill in the gaps with wood or small glass panes.
Next, my husband laid out the long 4x4 posts that we had -- as luck would have it we had 4 in the yard we could use... two we had purchased earlier in the year from a lumber store and paid about $30 total for those two. The other two were given to us. We laid out the 4 posts and he hammered them at the ends, using large nails and "toe nailing" them in at an angle to join the edges. The result was a "frame" on the ground that I think was about 12 x 8.
So far so good. Frank measured out what he thought we would need in terms of 2 x 4s. He looked at the way the "paper" windows fit, figured in the places each window joined another or hit the edge or roof, and then estimated the number of 2 x 4s he would need. For the front, being taller, it needed taller boards (I think 12 feet) and the rear needed shorter ones (about 6 feet).
We made a trip to the lumber store and spent probably about $150 on 2 x 4s. (I may be remembering wrong, but I think we may have had to run back out for a few more...)
We worked from the floor up, securing 2 x 4 into place and then putting a window into place and attaching the 2 x 4s to it. We used nails and some of the "v" shaped things you hammer in, I think. As each window attached, we put a 2 x 4 on the other side of it and slid the next window into place.
By some miracle, the windows and 2 x 4s fit to the inch! In case things don't fit exactly, you might want to have an extra 2 x 4 to put into the leftover gap.
Once the first level of windows was done on three sides, we put the second level of windows. Then Frank cut all of the 2 x 4s along the top to make the angle of the roof. We put 2 x 4 "supports" across the width of the roof and stretched plastic over it and stapled plastic down the sides to cover the remaining gaps. Again, if you want it prettier you might use wood or glass instead of clear, heavy plastic. Then we covered it with corrogated plastic roofing (?) to further protect it and nailed those sheets together and to the greenhouse roof supports.
We left a space next to a large picture window and that made the fourth, front side. In the gap, Frank "made" a door out of leftover pieces of wood, got two used hinges, and put plastic over the frame to make a door. If we had had a larger gap to fit in a door, we might have used a real door. But, due to the picture window we had been given, and my desire to use it, we had a very skinny door and had to make do.
The roof seemed hardest to me, because of the slicing to angle the roof. We felt that we had to angle the roof to avoid water buildup that could weigh down the roof.
I hope these instructions help. I wish that we had been able to retrieve pictures of the different steps of construction, as it was way cool.
OH... PS. Don't give it a floor. We made the mistake of putting in a fiberboard floor. You want to be on the dirt floor, and then cover it with gravel or something you want to walk on... don't give it a floor as the constant watering is weathering the floor like crazy... and the floor gives the snakes a place to hide!