I am doing a cake that is going to have a six inch top tier. on top of that tier there needs to be a cowboy hat. the cowboy hat will need to be about 4 1/2 to 5 inches around. would you make this from fondant, rkt or ??? does anyone know where i could possibly get a mold for about that size if I were to use fondant/gumpaste???

I made a hat about that size once and used RKTs inside the crown. I made the brim from gumpaste (solid, no hole in the middle) and rolled the edge and held it in place with paper towels while it dried like I wanted it. Then I centered the fondant/gumpaste-covered crown on the brim and held it in place with a little melted chocolate. It wasn't hard to do at all. Here's a pic, so you can see what I mean:
http://cakecentral.com/gallery/1718252/michael-jackson-tribute

Haha! now that I've looked at that photo again, I realize that I didn't roll the brim after all because I decided it would look too much like a cowboy hat. But the fact is you COULD roll it and hold it in place till it dried. Sorry about that!

Do you mean the brim will be 4 or 5" or the crown will be that sixe with a larger brim?

When I did mine I used two 5" round layers and a 1/2 ball and carved it. I made the brim out of gumpaste and rolled the sides on paper towel rolls to dry. Like Marianna, no hole, I set the top on the brim. If you're putting a 4 or 5" hat on top of a 6" tier, I'd allow several days for your brim to dry so it doesn't sag over the edges of the cake.

Here's a picture: http://cakecentral.com/gallery/2121521/ranchers-wedding-cake?sub=2121523

The one you see on the cake in my gallery I made from gumpaste, molded from a cowboy hat from the build a bear store.

http://cakecentral.com/gallery/2212125/buckaroo-cowboy-cake

Elcee and aprilismaius, LOVE those hats!