Hello Dynos,
I have a small question, so my code worked very well, but i get “imperial” values inspite of “metric” ones, why?
OUT = UnwrapElement(IN[0]).get_Parameter(BuiltInParameter.ROOM_PERIMETER).AsDouble()
How can i use the Units from the open document?
KR
Andreas
Revit API internal unit is decimal feet, you have to convert it either manually (there are dynamo nodes that convert values between units) or using DisplayUnitType api:
https://www.revitapidocs.com/2020/9cc2c0ea-f59f-9d76-ce19-ae7eede03bbd.htm
Heads up: I believe that this API changes pretty significantly in 2021.
Thank you … I use Revit 2018.3
I can`t solve it with any call for the current doc?
There’s no way around it. You’ll have to convert one way or the other 
OUT = UnitUtils.ConvertFromInternalUnits(UnwrapElement(IN[0]).get_Parameter(BuiltInParameter.ROOM_PERIMETER).AsDouble(), DisplayUnitType.DUT_METERS)
it worked! i just copy paste something, i want to understand
DUT_ stays for what?
Excellent
Display Unit Type is my best bet 
Tip: you can dinamically change to the “correct” type using the Parameter DisplayUnitType property