How much room is needed for them to fly down from the roost.

My girls jump off of our deck railing with a less than graceful thud! It is about a 4' jump. I figure that if they didn't like it, they wouldn't do it. If you have a ladder and they aren't using it, it would guess the same is true. They sure land with a thud though!

 

My roosts are about 4' high and they have about 3' of room to fly down. They don't seem to mind or have trouble with it, but at first I did put an old wooden step ladder with platform top nearby to give them an intermediate landing zone, and a few of them used it for awhile. When they stopped using it, I figured that was them telling me the flight down was fine.

 

Inside their chicken yard is a dead tree with branches going in 3 different direction...lowest branches are maybe 2 feet off the ground & highest branches are a bit over 5 1/2 feet. My chooks are 10 week old banties and several will jump up to the highest branches and then immediately launch themselves off into the yard...and then jump back up into the tree to do it all over again.
I've watched one hen do it 5 times in a row and two others play "astro-nut" (my term, don't know what they call it) three times in a row.