So I have a problem with Rhino :p

So a year ago i worked a bit with grasshopper and well i never really payed much attention to rhino itself, so i dont know how to use it that well, and I need help with that :p

Now i realize this is a grasshopper forum but I really dont know of another forum like this for rhino where the users are willing to help.

Anyways I have this project involgin a series of towers that join at the top to create larger spaces for commercial use, and well I cant join the shapes toguether... as soon as they get close they sort of cut themselves?

I just want them to join at the top like in the picture .