This house was shifted to one side of the lot because it had a side entrance garage. I remodeled this house to use the extra 18' to build a new attached garage to accommodate a workshop beside the front 2 1/2 spaces, and a storage stall one car wide forward of the outboard stall, and a porch off the rear wall that I was going to make into a greenhouse. Originally, The roof overhang you see was intended to be at the same slope as the glass would be, so the glass would butt-up to the roof and continue that pitch. But, they make houses differently now. The underside of that half roof just had the ceiling joists and was finished with aluminum soffit panels. I thought it would have 3/4" plywood across the whole surface with aluminum trim on that. They don't do that any more. That makes for more air passing through to the attic to cool the roof in summer. I suppose. But that meant that I couldn't seal off the greenhouse from the attic, and the always high humidity would have been catestrophic, creating a black mold haven. So I had to reduce the pitch of the greenhouse roof and terminate it against the brick with an open space so any heat or humidity could escape to the atmosphere, not to the house. But it looks funny.
Needless to say, snowload can be problematic and occasionally I have to trudge through a heavy snow at midnight to rake snow off the roof and the glass, too. Whenever we have a southeasterly blown snow that's wet, a huge drift builds up on the edge of the roof overhanging the glass. The original pitch and attachment at the roof would have eliminated the 30" step down from the roof to the glass. That step means that if a drift builds up and then slides off the roof it could crush the glass. No easy answers.
The inside dimensions are 6 feet wide by 21 feet long. It has a ventless gas heater, sink with hot & cold water, two waterproof florescent lights and two electrical outlets. I run a fan up high for constant circulation. The two lower left roof panels are hinged at the front glass and can open all the way forward (outboard, in front of the vertical panels). Usually, I just have them propped open about 4 inches during summer, and place screen panels on the six large roof panels to make it cooler. That works really well.
I started building elaborate coldframes out of old sash from the curbside supply store 40 years ago, so this is about my 6th attempt. You are looking at an aluminum box & angle frame to which are mounted 38" x 80" storm doors plus one door actually used as a door. The smaller roof panels are polycabonate. There is something less than $2,000 in aluminum & glass here. My final cold frame/greenhouse before this one was a lot higher class than #1 which was pretty crude, -all old wood, set on the ground at the head of my garden, and that rotted in about 5 or 6 years. #2 & 3 were wood, too, but a bolted assembly that I kept in the basement from June to March and assembled on my concrete patio each late winter. They lasted longer. #1 and 2 had flat tops and #3 had a 60° peaked top. Each one got about one panel bigger and more sophisticated. They all could be heated in the worst weather with one or two 150 watt lightbulbs in shop trouble lights. I could step into #3 & 4, and #5 was a real advance in aluminum with four door panels, as always from the curbside or dumpster hardware store.
The cement blocks were set on 12" square patio blocks and gave me plenty of room inside to walk down the center aisle. I heated it with one 600 watt calrod unit, ventilated it with an automatic bi-metal spring door. Both top panels opened entirely (just like #6, the current one). I had 2" x 12"s that married on top of the open hinge panels to give me two good perches for plants out in full sun. Not having the passage through the cement block was just a matter of it being a whole lot easier to design & build. They don't make block in sizes that I could combine to get the dimensions I needed, so I just did it the easy way which I do not regret. The door was high enough so it never got snowed shut! This is a dry block assembly which does not frost-heave. (The tall chainlink fence lines you see in the background were permanent trellises for peas, cukes, squash and tomatoes. They too, came from junk at construction sites, along with the cement feet attached, that I dug big holes for and were an innovation worth remembering. I now use a smaller, moveable set of chainlink panels rotated from bed-to-bed for snap peas, and have fixed 2" pipes in 3 beds that I attach to with zip ties, and two 12" square x 7' tall box aluminum frames that also rotate for tomatos and cukes.)
This is an assembly that has only 12 SS bolts and 4 hinge pins holding the six panels together, so when I moved to my new home, I gave it to my sister.
When my sister's son got married to a gardener, it disassembled once more and now another budding gardener has a neat tool!
Build it, and they will grow!