OK. This one is not a catenary arch. Nor is it precast and moved into place with the tractor. This on is old plain old fashioned build forms and pour concrete. Used about 600lb of rebar, and around 18000 pounds of concrete. It ain't going anywhere. The concrete vendor, Block Sand and Gravel, delivered the concrete too wet, (and without the fibers I paid for...). You could really tell this durring the first couple feet of the pour, as besides being quite runny, the extra water seeped through the OSB... You wouldn't want to use 1/2" OSB for one of these forms if you were going to use it more than once. Interestingly, the inside of the forms were baby face smooth, but the water in the concrete caused the wafers in the waferboard to expand and give the concrete a dandy OSB look to it. A coat of paint on it and it looks just exactly like the the wood rooms beside it.

Left two are pictures of the back wall form, and the wall rebar. Right is a picture of the steel door frame.

Left is a picture of the pipe I put in the wall to make holes for air vents. Center is my daughter helping tie the rebar for the roof. I kind of went overboard on the roof rebar, it's every 6 inchs. Right is the forms just before the last wall went on. I have since pulled all the forms and re-used the plywood for the office and the paint room.

Left is a picture of the completed form. Middle is a shot of some of the bracing. I figured out that my roofing nailer would shoot right through 20 guage sheet metal, so I went to town... Right is a picture of the bracing for the roof form durning the pour. I jacked the center of the roof up about 1/4" before putting the bracing poles in. Cross beams are from the wood drying stacks in the greenhouse/kiln, vertical poles are a left over 5x5 from the main shop, and the wedges were cut on the bandsaw.

Having your own sawmill is handy...