Here are some examples of crowns and coronets, which are much like circlets, except that they have raised portions, and are not defined as only being worn by Lords and Ladies. Most nobility have historical examples of how the crowns and coronets should be made, but they aren't hard and fast rules. Do what you want, be creative, be flurby.

Here is a crown made by Callandra for our Duchy, Phoenix Tears (It might have been a Shire or Barony when she made it though). You may consider this a circlet, cause it only has one point sticking up, but I would say it is a crown, only because it bears the heraldy of the group, a teardrop in flame, so should be a crown of the group.