I did a quick google search on "chicken housing area". It seems the general thinking is that for standard sized chickens you should allow 2-4 square feet per bird for the coop, and 10 square feet per bird for the run. You can do the math. If your hens are likely to have many days when they are stuck in the coop due to weather (mine, for instance, refuse to dirty their feet on snow, so they have spent about a month without going outside no matter how many times I open their door!), then I'd imagine that a larger allowance is good. On the other hand, if the only time they'll be spending in the coop is when they're roosting, you can get away on the lower end.

--Johanna

I have not had my chickens out yet as they are chicks right now. But from raising roller pigeons which I still have, birds are very easy to train to do what you want. They will probalby feel safe in the hen house if that is where they have been roosting. But you could get them hungry one day before letting them free range and then feed them a little here and there to keep them close to home, but do not feed them too mucha and in the evening feed them in the coop to get them back inside at night. Once you do this for several days they will automatically go inside i would think. Once they have estabished the hen house as home that should stay home for them. You can cut the feahters off one wing and that will prevent them from flying up into trees but you will need a latter for them to walk up to the roosts. If you have a rooster he will help keep rodents away and alert the rest if a hawk is flying over head. I think most of them will stay in a group for the most part and if you let them out on a day when you are there it will be best.
Also when you feed them call them or whistle or shake a feed can with grain in it, this will instill in their minds that noise means food and it will help you get them inside once you let them free range. I haven't had chickens but this is the way I train my roller pigoens to return to their pen and they go in right away after flying to get food. Bill C

First, no need for training, instinct will get most chickens in the coop at night. A rooster can help with this at times, making sure everyone is in for the night.

Second, I would personally rethink not having a run of any kind. There will inevitably be times that you want to keep them confined for a day or a few hours etc. Either due to weather, or your not being home etc. Or you are having a farm party and don't want chickens on the picnic tables, what ever things will inevitably come up. Also if the run is secure this allows you to have a bit more flexibility as to what time you get out there to release the hens. With this set up you can leave the door from coop to run open, you then only have to open the run door to let them free range. If you are primarily letting them free range then the run doesn't need to be as large, it is more of a holding area, not a living area.

If you build a new set up with an attached run, this will allow you to keep them in this space for a couple days until they imprint on it. After that settling in phase I wouldn't expect you to have any issue with them coming to roost at night.

Kat