@JetFighter I will explain it here, and then make a build to show you.
1-build the base. This is the basic shape of the roundel. Most roundels have their design on a circle, or oval.
2-build the next largest piece. This is usually the most important part of the design. It is the easiest part as well. Use one piece to get the basic shape.
3-repeat step 2 if needed.
4-add small details one piece at a time. When adding small details, like points on a star, it is best to make them one at a time.
The next step is for wing roundels:
5-nudge everything down to the base. Make sure you are able to see the design, but it shouldn't be sticking out by much.
The next step is for Fuselage roundels. Ignore the previous step:
5-use fine tuner to scale. Uncheck the box that says scal only selected part, and make it about .2 of its default thickness.

Thanks @KnightOfAraluen . I already have both mods. You of course can teach me how to make the USAF roundel, Squad roundels, etc.

@JetFighter I would, but now that I am looking at some pictures, most of them don't have roundels. The ones that do, the roundels are too blurry for me to see. I can teach you how to make roundels if you want. You need to be able to nudge though. I see you are on Android, so get fine tuner and overload if you haven't already. They will help a lot. If you need help doing that too, I can help.

I can't make the roundel very good, but can you make it @KnightOfAraluen ?

It looks good, but it could use some more details. Air force roundels would be good.