You can get packs of cheap craft paint brushes and use the bristles. Remove the metal ferrule, to remove the bundle of bristles. On many of the brushes, the bristles are attached or adhered to a membrane or a coating and can be "unrolled" into a long strip. Attach these to the roof of your build, starting with the bottom course and working your way up to the ridge, just as on a real roof.
Prost!
Brad
I make mine the same way and then rattle can it with some cream/beige, then i wash it with some diluted black paint for that aged look.
Coconut fiber out of hanging baskets works well as well.
Matt