Ann Arbor has some paved "multi-use" trails reasonably well-suited for skating.  They are listed in the City of Ann Arbor Bikeway System map:  http://www.a2gov.org/government/communityservices/ParksandRecreation/Documents/bike.pdf

The best paths can be reached from Gallup Park.  There are two good places to park at Gallup, either the parking lots reachable from the main entrance:  http://maps.google.com/maps?f=q&hl=en&geocode=&q=3000+Fuller+Rd+Ann+Arbor,+MI+48105

Or at the UM Mitchell Field parking lot: http://maps.google.com/maps?f=q&hl=en&geocode=&q=3000+Fuller+Rd+Ann+Arbor,+MI+48105

The Gallup Park main building has bathrooms open year around, but the parking lots can be more crowded during prime time.

The Washtenaw Border to Border (B2B) paved trail runs from U Hospital (Fuller Rd and Maiden Lane - just west of Mitchell Field), through Gallup Park, out to the area of Golfside & Washtenaw in Ypsilanti. The B2B brochure is here:  http://www.a2gov.org/government/communityservices/ParksandRecreation/Documents/bike.pdf

I really like the section east of Gallup Park - just skate up out of the park up onto the Dixboro Bridge and continue on the path, past Washtenaw Community College, around St. Joe Hospital and past the EMU athletic facilities.  The pavement is fairly good and it's generally pretty empty, unlike the section in Gallup Park.

I also skate on the multiuse trails along Plymouth Road between Maiden Lane and Green Road and on Huron Parkway (east side of the street).  Huron Parkway crosses the trail right next to the main entrance of Gallup Park, so you can easily skate onto the trail from the park.