Building loft within existing room

[ever0095]

My layout includes 14 foot ceilings with a lofted area near the center of a long/narrow stretch. The floor of the loft is right around the 7 foot mark, but I can't determine how to create a room and new ceiling/floor within the existing floor's layout. The attached image is as close as I can get - if I try to change the small room height specifications, the out wall of the entire layout if screwed up.

What's the best way to create a room within a room like this? I'll then need to be able to work on the layout of the lofted area itself, and the loft overhangs the enclosed room below by 3 feet or so.

Thanks!