Gee, 'before' takes all the fun out of it, and you won't get to invent nearly so many new expletives that way LOL
-concrete floor or raised wooden floor? And, would it be benificial to cover the wooden floor with galvanized sheet metal?
Largely depends on how pricey you want your coop. Concrete is awfully nice (except in hot climates) if you can afford it but it sure is expensive if you have to pour new. Raised wood floor is fine as long as it is raised high
enough not to provide a nice nook for vermin to set up residence. A dirt floor is not such a terrible thing either, though, unless you really expect to have significant rat problems.
I seriously doubt it is worth the trouble and expense of covering a wooden floor with galvanized steel - especially since as soon as the galvanized coating gets scratched through it will start to rust anyways. If you are seriously worried about rats digging in, shell out for a concrete slab; if you are just worried about other digging predators such as dogs and coyotes and foxes, use a dirt or raised wood floor with good predator-proofing around the perimeter.
-I want to collect the rain water from the roof for watering the garden, is it safe to give the the rain water to the chickens?
What will the roof be made of? I would not give thm water off an asphalt-shingled or tarpaper roof, which will have all sorts of nasty stuff dissolved in it. (I am sure there are people out there who do it and have live chickens, but I sure don't think it'd be a good idea to try). Galvanized roofs are questionable for long-term drinking by people but probably not the end of the world for livestock. A painted steel roof should be pretty much ok.
However if you are going to use the water for the chickens, especially if you are going to be storing it for any length of time, you might want to look into designing some sort of system (tip bucket or other) that will discard the first flush of rainwater off the roof, which will contain the highest amount of contaminants from dust, bird poop, etcetera. (Raw roof runoff, especially once held in a cistern or barrel, can have bacterial and parasite contamination issues.) You can probably get away with them drinking roof water if you need to but if you have the choice it might be better not to.
-Is it neccesary to insulate the walls and ceiling? (i live in michigan, a couple of weeks ago it was -10 degrees with a windchill of -30)
Yes.
(But do make sure you build in lots of ventilation, too -- you can always close it off on the coldest nights. Insufficient ventilation is bad for chickens' health and will give you a stinky damp coop).
Have fun, the snow will not be around *too* much longer
Pat