In a bowl, mix together water, buttermilk, sugar, melted butter and yeast. Allow to sit for 15 minutes..
Add in salt, eggs and flour (for flour, be sure to spoon in and top off and start with 4.5 cups - you want the dough to be sticky). Mix for 10 minutes and allow to rest for 10 minutes.
Prepare your filling by mixing together melted butter, brown sugar, sugar and cinnamon. Set aside.
On a floured surface, roll dough into a 12 x 16 inch rectangle.
Spread your filling over the top and roll up. Cut into 12 large rolls (or 18 smaller rolls).
Place rolls in a large, greased baking dish or jelly roll pan.
Bake at 375 for 15-20 minutes.
While baking, mix together your frosting ingredients. Spread on warm rolls. Add another layer of frosting once cool.