Be sure to check the rating on your extension cord!!!! Cords are made with different insulation materials, wire material, wire gauge/ thickness, and also length.
*** Length decreases cord capacity, multiple cords in series can be VERY VERY dangerous***
Consider the following:
If you attach 3 150-Watt lights, 1200-watt stock tank (water) heater to a standard 25' extension cord... You may be readying to burn down the coop. Especially if your coop is 60' from your outlet and requires 3 25ft extension cords in series!!!!!!!
Be very careful with electricity!
Read the tag on you extension cord to see the MAX you can run through it AND do not use multiple extension cords.
Do not try to be ChevyChase from NationLampoon'sChristmasVacation, you don't need 400 outlets, wires, and surge protectors to heat your coop. Otherwise it may end up like the cat! (Movie references)