thats almost my exact scenario right now, its really too hot in the garage during the day and theyre just over a week old .. they need lots of water if its hot ... the plan is two-fold depending on weather ... tomorrow theyre going into a wire pen in full shade out back, covered with a piece of tin, secured with a cinder block on top .. highs are in low 90's in the day, and 65-70 at night, so at 1-2 weeks, i should rotate them back to the box in the garage where temps will likely stay above 75 at night, they wont need additional heat if theres no draft .. after 2 weeks they can stay in the wire pen 'covered' by a sheet at night to block draft if these conditions hold, but if it cools below 65 or it rains etc, i'll rotate them back to the box at night .. after 3 weeks they can pretty much stay in the wire pen no matter what, still cover it with a sheet and secure it well at night .. be sure its weighted down with a cinder block or two so racoons etc cant tip it .. move the pen around daily and wash the spot in with the hose and it gets easier from there .. start training them with food, feed and lock them in the coop while the others are out etc .. not too much food, you want them hungry again to go back to the pen, by 4-5 weeks you can get them to go anywhere you want without grabbing them and everybody is 'on the program' lol ..