Help me set up my grow room

Ok..I am currently looking to grow 4 plants (some seeds found in some pretty good nug I had 2 oz of)I am going to purchase a complete grow kit from htgsupply.com
which includes: HTG Supply Ultimate 400 watt HPS & MH Grow Light, 400 Watt High Output HPS Bulb, 400 Watt MH Conversion Bulb, Dual Outlet Mechanical Timer, High Low Reflector Hangers, 100% ORGANIC ADVANCED NUTRIENTS IGUANA JUICE by Dr. Hornby!, Advanced Nutrients OVERDRIVE Ultra Premium Liquid Flower Enhancer, 1.5 cubic feet 100% ORGANIC FOXFARM Ocean Forest Potting Soil, 9 TWO GALLON Grow Bags, GrowBright Thermometer / Hygrometer $275.00..
Im wanting to set this up in a buddies garage and im not sure if i will make a grow box or just have it on the floor..
The only problem i can really think of is i live in oklahoma and the winters can get kinda chilly will it be to cold for the plants to thrive? If so would a grow box help?
Anything else I should put into consideration before buying all this?

Well it depends a lot on how cold it gets in the garage. Depending on how well (or poorly) insulated it is, whether it's attached to a house, and stuff like that you lights may put out enough heat or you may need to get a space heater to make up the difference.

An insulated grow box could make it much easier.

Beyond that it sounds like a pretty good setup.