Terry, this is a great topic. Your going to get some differing opinions..
I've lived in the Mid-West my whole life and a big part of that has been spent dealing with snow and I know Wisconsin is on a whole other level. This one element alone has made having a garage important to my tenants. I mean who likes having to go outside and scrap off they're car at 6AM before heading into the office? Snow is not the only reason but security. Though the area I own in is safe it provides both the tenant and their property another level of security and peace of mind.
I own a duplex and charge the tenant using the (1) car garage $100 more a month. Not every house in my urban/yuppie part of town has a garage but I think the fact I have one helps me compete with the new apartment/condo complexes popping up all around me.
I'm not sure what it would cost to have a new constructed garage but considering your climate and how much more you can charge ($100 in my case, I've heard of even more). I believe the additional income would cover the cost in no time.
I hope this helps Terry. Best of luck.