If you make the lid out of the top third of a drum, make the cut below the highest point of the rib. Then pound out the lip and you have a nice tight fitting lid. The widest part of the rib will be what actually sits on the lip of the drum, and you will have a nice lip that extends down past the roll of the drum top. The first one I made, I cut just at the widest part of the rib and it doesn't have anough of a lip to sit right, it is easily bumped off and hard sometimes to get on good. With the longer lip it is much more stable.
Takes a little practice and you need to make the lid for the drum you are going to use the lid on. I made one at the shop and it fit that drum great but it wouldn't work on the drum at home. had to open it out some more.