I'm asking for help and explanation how to made some unique buildings common for more than one nation.
I would like to have in game Arabians and Ottomans both possible to made Madrassa and Hammam for example.
Greece and Rome both to share as common Forum and Odeon.
Acctually UB to be grouped not only by one nation, but by flavoures that existed in CivIII MidEast, Mediteranian, American, Asian civs to share there unique buidings among themselfs...

Thanks.

In the civilizationsinfo.xml, simple add another unique building - cut and paste Arabian UB and give it to Ottoman, and vice versa.

Unique Building is a mis-nomer, the only thing that make them that way is the XML file listing it in only one spot, at the code level all this stuff is "default replacment" meaning that each Civ get that instead of the normal version, nothing makes it unique to them and any number of Civs can also use it as a replacement.