Silkies can’t fly so they will need a ramp. Even chicks two weeks old of breeds that can fly shouldn’t have any real problems flying up a couple of feet if they really want to. Most full sized grown chickens I’ve had would prefer to jump/fly down from two or three feet instead of use a ramp but some will. You can make it easier on them if you wish though. They might or might not use it.
I’d suggest a 30 degree angle on a ramp. For every one foot oh height go out horizontal about 1.7 feet. That will be close enough. Just put a few strips across to help them get their footing and they can easily use that. I know some people use steeper ones and they work but you wanted a suggestion. No matter what number anyone gives, someone will come up with a different one. A lot of different things work.
You could also build a series of steps out of wood or stack cinder blocks, something like that. Some will use it and some will ignore it.
For a two foot or a three foot height, you probably do want to do something.
