Problem: Revit 'Roof: Gutter' tool only works on horizontal edges. How do I model a gutter on a sloping roof edge? For example a skillion roof with a 45 degree edge.
Applies to: Revit 2014. but probably applies to all previous versions too.
Solution: Use 'Model In-Place' with a sweep and use "Pick 3D Edges".
Step 1: Model your roof, in this example a skillion roof with 45 degree edge
Step 2: Architecture Ribbon > Component > Model In-Place
Step 3: Select 'Roofs' category
Step 4: Type 'Gutter'
Step 5: Create Ribbon > Sweep
Step 6: Modify Sweep Ribbon > Pick Path
Step 7: Modify Sweep Ribbon > Pick Path > Pick 3D Edges
Step 8: Pick the edge of your roof where gutter to be located
Step 9: Click green tick
Step 10: Modify Sweep Ribbon > Select Profile
Step 12: Adjust the X and Y position to suite. Use flip button to get the gutter showing the correct way up
Step 13: Click green tick
Step 14: Click green tick to finish model