Please ignore - user error. I have to say these are a little complicated to do first time around and mistakes are a little too costly.
Doing my first one of these and I am not getting anywhere to put the very last building. According to Evil J's adventure guide I should be able to put it on top with the other two but there is just no spot that it will accept either the PH kit or the Watchtower Construction Kit.
I am not going to be happy after all that killing not to be able to finish this.
https://imgur.com/a/uTkteG0
this is the map as I have now and the two buildings placed on top - armory and headquarters