my plan is that when i draw a model line, dynamo will pick the right family. for an example: if the line is 10m, the correct family where the length is 10m will be placed in revit.
Welcome @Djurrelankhorst to the Dynamo forums.
What is your question exactly? Are you stuck with your graph?
I’m totaly new with dynamo. And my assignment is that I have to make an dynamo where dynamo will automaticaly pick the correct family when a line is xxx meter.
But i dont know how to make it, so if someone can help me.
I suggest this link for starters.
On these forums it is usual you put in some effort yourself first.
Have something to show etc.
No point if people just posting the solution. You don’t learn much from it.
Also you might bit more of than you can chew for your first Dynamo graph.
But to get you starterd; look into the nodes containg 
in the nodes title;
- Get Parameter Value by Name
- Curve
- Start Point
- End Point
- Boolean Mask
- Model Categories
- Get Location
- All Elements of
- Sort By