Dear Dynamo Specialists,
I have a lot of rooms where i would like to create a (detail) line raster (for automatic dimensioning this appartment) on the total appartement. I would like to create a set of lines (yellow of second picture) from the room lines to a border set of lines.
Could anyone help me?
Why not snap to the elements which define the collection of rooms instead of adding bloat to the model and creating situations where you’ll have to make the same change in multiple locations due to the detail lines?
All of those dimensions can be drawn from element to element though.
Just because Dynamo can do something easily doesn’t mean we can discount best practices for modeling. Adding the lines is just going to make things inaccurate over time as the person who moves wall X to account for a fire assembly change won’t know they need to move your detail line.
Look into getting the boundary curves at the finish face of the wall. Generate a sample point on the outside of that and test if the room at that point is in the same unit; if not, you’ve got a perimeter wall - keep that line. If so, discard it. Then generate the detail line on all remaining curves.
Not an easy graph to build, but not overly difficult either. Give it a shot and see where you get. If you get stuck post back and the community will try to give you some direction. 
Agreed. I have / work on something similar.
I have waaaay more difficult times when trying it on outer Walls (facades).
Facades can be build in so many ways with Walls.
Things to take into account then;
Wall Joins at corners (order - which comes first).You can also have a look at this 
.