So here it is, the first sketch taken right from the above link. First I outlined the bud and then added the details.
It didn't take me very long to complete, although I must admit, I wasn't in a rush at all. Looks a bit schematic, but that's the reference.
Of course, since these were the photos of a real life flowers it took me a bit longer to sketch. Some of them I redrew several times, but I think it was worth it.
Many more sketches followed these one's. I actually had fun using this method and right now I have about 15 sketches of different roses. It's not that much, but I'll keep practicing and I hope you do too.