Chicks will be ok outside provided you have a good, draft free place to keep them and provided you can keep the temperature under the heat lamp where they need it to be for their age.
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I'd be careful with straw. It catches on fire from headlamps. I put chicks in a stock tank. I put a heat lamp in about 12 inches high. I then cover the tank with a piece of tin. I have several hundred brooding this way in several tanks. We do well with this set up in Colorado random weather.