7 stud curved lego train roof

Found the inspiration for this smooth curved roof by experiments conducted by raised;

 

www.flickr.com/photos/raised/albums/72157687411034970

 

Vents can also be incorporated by substituting the 2 rear Slope, Curved 2 x 2 for Slope, Curved 2 x 1, 2 x 1 tile.

 

 

 

Done