I keep my brooder in the coop. If you can keep one area of the brooder in the recommended temperature range (which means electricity and a heat source), keep them out of drafts, and keep them predator-proof, it is absolutely doable.
I'll spout the party line. Chicks need temperatures in the range of:
90 to 95 the first week
85 to 90 the second week
80 to 85 the third week
75 to 80 the fourth week
70 to 75 the fifth week
After that, they are fully feathered out and do not need any supplemental heat. I usually turn my heat off after four weeks, but I have several chicks that can keep each other warm if they need to.
They do not need their entire brooder this temperature. I keep one small area of the brooder in that temperature range and let the rest be a lot cooler, even 25 to 30 degrees cooler in the far corner. They roam all over the brooder and go back to the heat to warm up when they need to.
If you have a lot of chicks, they can pile up and keep each other warm. With only two or three, the pile is not that big so you might need to watch this closer than some of us. But I think they are a lot better off if they can pick their comfort range.
Please take any recommendation you see as a general guideline, not as a hard and fast law of nature. Chickens are adaptable and will do well in a wide range of conditions. We all have different circumstances and many of us violate some of the generally accepted guidelines and do OK. These guidelines do not guarantee absolute success if they are followed nor do they guarantee absolute failure if you don't follow them exactly. They are intended to improve your odds if you follow them. So treat them as a target and try to get close, but don't panic or stress out too much if you occasionally miss a little. Chickens are supposed to be fun, not stressful.
