Hi @Daan,
Thanks! 
I’ll try to make myself clear as much as I can. I’m looking for a script to make join elements of two categories that intersect in a specific order (e.g. if I join slab and beams, I want the slab to cut the beams; viceversa if I switch join).
I only found ways to make elements that intersect join in a random order and I thank Ammo for this because his workflow from this post ( Auto join Elements - #10 by ammo ) joins interesect elements very fast in my project.
I was not able to figure out the switch join order thing.
I’ve read tons of post on this forum, watched tutorials without any result.
Sorry if this question might seem stupid, I’m trying to learn as much as I can about Dynamo and I’m doing my best. I would really appreciate any advice.
Thanks in advance for every minute of your time,
G