I have an 8x12 main coop on the ground, a 4x8 shelter on the ground, and a 4x8 elevated grow out coop. Getting them to go into a ground level coop has not been much of a problem. The elevated one practically always is a problem.
I've had 2 week old chicks fly up to a roost when their broody told them to. Some had problems but most did not. I've had 3 week old chicks play on roosts 4 or 5 feet high during the day. They wanted to play up there so they flew up. Having Silkies or Frizzles that can't fly is one thing, but the vast majority of pretty young chicks can fly pretty well if they want to. The trick is getting them to want to.
I started using a tree limb as a ramp. Some would use it to walk up or down, many would fly up or down. They did enjoy perching on it during the day. I eventually built some steps for them with the same results. Some would hop up or down but many would fly.
When I moved chicks to that elevated coop I'd generally house them in the coop only for a week or more, hoping they would see the coop as home and put themselves to bed. That works for my ground level coops. But with that elevated coop it never worked. I'd come out at bedtime to shut the pop door and they would be in a pile under the pop door. So I'd do what it sounds like you are doing, lock them in the coop. My typical brood was around 20 chicks.
One time they all put themselves to bed on their own their second night in the run. A couple of times I had to be down there every night for three weeks before the last few finally got that message. Most of the time a few would start going after the second or third night I put them in and all were going in after a week but each brood could be wildly different.
In my opinion, if they want to go up there they will whether they have a ramp, steps, or have to fly. If they don't want to it doesn't matter what they have. Be consistent in putting them in every night and they will eventually want to.
Good luck!
