Okay, I'm making a cake of Captain America's shield for a groom's cake for tomorrow. It's a fairly simple design. My only question is how would I go about cutting the fondant rings (2 red, 1 white and a blue circle for the center) and lay them to fit perfectly? Is there some sort of ring cutter (if that makes any sense)? What is the best way to approach this? I'll try to attach a pic of the shield. Thanks!!!
ETA: It has a dome-shaped top, so it's not a flat circle, if that makes a difference.

I think your best option would be a set of nesting circle cutters. I remember seeing one in the last couple of days, but I do not remember which site I was on. Another option would be to use a compass to draw the circles, then cut a stencil out of paper or thin cardboard. Lay it on the top if your fondant and cut out the circles.

Use different size glasses

Is it going to cover the whole top of the cake? I've used my cake pans as templates to cut out the brim of the top hat on one of my cakes and the top of my graduation cake. Maybe try that? HTH.

Well, I would definitely do the cake in red and add the one white ring and the blue center (thinly as possible) on top of that.

I would take the pattern and enlarge/decrease with the copier to the size I needed and cut out my pattern to lay on my fondant to cut out. Use a pizza cutter or exacto knife.

To keep from distorting the rings, I would make one disc out of white then mark off the rings and star. Apply disc to cake surface. Then, carefully paint the appropriate areas.