Keeping babies in a section of the coop?

Jessie, that's exactly what I have been doing in CO for the last two weeks.  I sectioned off a 3' X 3' area of my coop, made a brooder with the top and one side covered in plain old chicken wire, the other sides in solid sheathing, hung a heat lamp and put in a waterer and feeder for the chicks. Nothing fancy, even the measurements on the sides are not exact.  Pine shavings on the floor and a piece of 2 X 4 with the 2" side up just laid on the floor for a somewhat elevated roost.  Our temps here at night have been as low as zero but averaging in the low 20's, and during the day have ranged from about 30 to tomorrows beautiful predicted 68.  At night I cover the 3 X 3 brooder with a piece of solid sheathing to retain heat.

I have it easy in that this is a new coop with no other current occupants, but I believe this setup would work even if I had other, older birds, and would also allow them to become familiar with each other before I released them into the existing population.  In fact, as I have two more batches of chicks coming in over the next 3 weeks, that is exactly what will happen.  The older chicks will be released into the main, open part of the coop while the new chicks will go into the brooder.

Good luck with your chicks.

I went out and took a pic of my setup to make it a little more clear.  Depending on the size of your coop or the number of chicks you are brooding, of course you may need to make adjustments.  I'm sure people have better setups, but this works for something I only use once a year.

ETA:  I have added another 'roost' to give them a little more height at 3 weeks.

at what age should i be putting in a roost board ?

I don't know about 'should', but the one 2 X 4 that sits on the floor and so is elevated about 3 1/2 inches from the surface I put in the day I picked them up.  They have been sitting on it since they were about 4 days old.  I don't think they sleep on it or spend hours sitting there, but they did seem to enjoy having a place to hop onto.

the little 2 X 2 that is angled up from the floor to about 1 ft hi I put in at about 2 weeks and they actually spend a LOT of time on it.  Last night they slept there for at least a portion of the night.  

When I put them out of the brooder, either this week or next, they will have a 3' high roost with a ramp up to it.  If I find they don't make their way up to it, I will put up a temporary roost at about 1 ft.  None of this is 'cause someone told me to, just seems practical based on their present behavior.