They can leak at bolts and seams. If a few leaks are going to be show-stoppers for you, reconsider the quonset. I chased leaks for weeks on mine.
Don't use adhesive like 3M 5200. I did, and it was a bad idea. The adhesive locks in any deformities. Use butyl rubber calk. They may tell you calk is optional, but use it.
The bolts come with a hard rubber washer. You need to tighten the bolt until the washer just starts to deform, and no more! Every bolt you over or under tighten will leak. Unfortunately, you will sometimes have to tighten them much tighter than that to draw panels together. Have a bunch of long sacrificial bolts to draw panels together. There will be thousands of bolts, and dozens of leaks.
You will need to assemble the hoops on the ground, then stand them up. They are limp like cooked spaghetti until you have several up and bolted together. Plan to rent a zoom boom to stand up the hoops. Plan to rent a scissor lift to work the under side. Once you have three of the hoops up and bolted together, you can climb on top to work the top.
My 30' by 49' by 16' high quonset had 120 panels in 24 hoops, with about 4,500 bolts and nuts. Every bolt had to be tightened exactly right. I thought it was going to be quicker and easier than frame construction. The second one would probably be no harder than frame, but the first was definitely harder for me than frame would have been.
