Suggestions for modeling 2nd story addition on garage (deck style, on posts)

[mpetrucco]

Hello. I am a relatively new user and am still learning. I am working on plans for a 2nd story addition off the back of a two-story garage with gambrel roof. The addition will be off the back, gable end, and is planned to step down approx 14" (two steps down into the addition bedroom) from the second floor living space above the existing garage. The addition will be a 16x18 bedroom added to the upstairs apartment of the garage).

 

I was able to as-built the existing structure and gambrel roof and the roof planes seem to match existing quite well. For cost-saving, the 16'x18' bedroom addition will be supported by posts much like a second story deck would be. 

 

My challenge is that the floor level of the addition will be set below the second level by approximately 14" in order to bring the roof line below existing. Can anyone help with suggestions on how to correctly approach drawing the addition? Would it be best to treat it as a deck or porch? Or draw standard 6" exterior walls for the three new exterior walls and manually draw a gabled roof? In my attempts so far, the wall approach is creating issues. The roof is drawing higher than the wall top plate and I am not sure why. 

Any tips for the best approach on modeling this addition?

 

The attached photo with the grey buidling is a concept sketch from another software. The one with the blue building and added deck is a start of an as-built in Chief of the existing garage (24x28'), with a deck added as a first try at the addition. Notice how the attic space framing and siding have dissapeared by adding the deck (another issue I need to figure out)

Edited 4 hours ago by mpetrucco