I just kept 14 chicks inside my back room for about 4 weeks. At that point we couldn't take it any longer, and now they are in the garage. I got a very large box (about 4x4) and lined the bottom with non-slick shelf liner. (A sort of foamy kind.) Then inside the box on top of the shelf liner I put a 2x2 ft. wire rabbit cage for the brooder. I set a 250 watt heat lamp with a red bulb on top of the cage, and it had a dial on it so you can adjust the strength of the light. I had a digital thermometer with a probe, put the probe right under the light on the bedding. For the first week or so I kept the wire cage door closed, chicks locked in there. I lined the bottom of their cage with newspaper and paper towels on top of that to prevent slipping. After that week, I put in low dust pine shavings and opened the cage door so they could explore out into the box and have more space to grow. They cost very little to raise. The pine shavings are about $5 at Tractor supply, and one bag will last awhile in a small indoor enclosure. The heat light bulbs last forever and are about $4 each. I feed mine fresh ground feed from a local feed store and it's $4.25 for 25 pounds. The 25 pounds has lasted 4 weeks now, there's still about 1/3 of the bag left.
As for keeping chickens inside past the first delicate weeks of life, I would not recommend it! Chickens are just dirty creatures, they can't help it, but they are gross. Even my chicks produced enough dust to totally coat everything in the room we kept them in. I'm sure larger chickens inside will produce much more dust. Even if you clean regularly, older chickens make big smelly, crusty poops. They love to scratch for bugs and take dirt baths, eat weeds and sun bathe...I can't imagine depriving them of all that. They are livestock, after all. What does a healthy adult chicken do inside? Sit around? Seems like a sad existence to me. It would be like having a large dog in a tiny apartment and never walking it or giving it a chance to burn off energy like a normal dog does.
As for keeping chickens inside past the first delicate weeks of life, I would not recommend it! Chickens are just dirty creatures, they can't help it, but they are gross. Even my chicks produced enough dust to totally coat everything in the room we kept them in. I'm sure larger chickens inside will produce much more dust. Even if you clean regularly, older chickens make big smelly, crusty poops. They love to scratch for bugs and take dirt baths, eat weeds and sun bathe...I can't imagine depriving them of all that. They are livestock, after all. What does a healthy adult chicken do inside? Sit around? Seems like a sad existence to me. It would be like having a large dog in a tiny apartment and never walking it or giving it a chance to burn off energy like a normal dog does.