1) Anyway I was reading somewhere else that you where only supposed to have them 12-18 in of the floor of the coop. But, by looking at pictures of other peoples i have noticed some to be as high as 3 -4 ft from the floor bottom.
The height is very much dependent on the breed. So decide now on what breeds you will keep. At the riskl of repeating Jody's excellent comments, heavies should be a little lower to the ground, say 24." Lighter breeds can be higher. As a good compromise, I'd suggest 24-36" and give them a ramp to get up with. Chickens will roost where they like, not always where you give them space. you have to decide what you want them to do and then make it so that cant do other things.
Chickens arent as bright as we think and they pretty much do what they want. Maybe I should say that they do things we dont plan for and that which they are able to do. Roost high in the rafters? Sure, if they can comfortably get up and down again. A way to keep them off the nests, and anything else you dont want them, on is to place a slanted peak on top. I hinge mine against the wall. The chickens cant hang on to it and soon give up trying - and I can put stuff behind it as storage.
2) ONE MORE THING! I have an idea of making "ramps" that go up to the top of my coop. So the hens believe they have more space to roam then they really do but my question is, "can i do this? is it safe for them?"
I know people do this and it wont hurt the birds, especially if they can clamber up and down your "jungle gym" without having to fly down. Again, the heavies can have their legs harmed by essentially "free-falling" to the floor.
But, remember, unless you live in the Arctic, the coop is a place to roost and lay eggs, not loaf around pooping all over chicken gyms. Yep, the more stuff you put in there, the more stuff you'll have to clean. <<< Okay, sorry, that was my PERSONAL view. Lets try this again, shall we? >>>
In the cold countries that gym contrpation might be a good idea, if you have the room for it. Since they may have to spend more time inside than birds in warmer climes, the diversion might do them some good. I suggest you make it dismountable so you can take it out and clean it. When the blizzards have passed.