OP, I did a tier like the one at the bottom.
It takes a really long time to do, so make ure you allow a few hours.
I'm not sure if this is how others have done it, but I used a 50/50 mix of gumpaste and fondant, rolled really thin strips and just started in the middle of the big roses and rolled them around, using tylose glue at the base of the strips. I did them flat on the bench and let them dry for about an hour or more, until the strips were a little bit stiff and the glue was tacky before lifting the whole thing up onto the side of the cake.
I found that as I went around with the strips, the base where I was attaching the strips to the inner layer would become smaller than the top, so I rolled a rope of fondant and attached that at the base, before continuing with more strips.
Let the rosettes dry on the cake for a while, then starte filling in with more strips. You'll need kicthen paper, or plastic wrap to help the strips hold their shape while they dry.
You need to roll about 16 million strips. It's a really good workout for the arms and shoulders.