My suggestion contains of a Tribe Wonder which is available to every Tribe.
The Idea would be pretty straight forward to implement since is not a building. Will be only a new tab in the tribe menu.
Developing Tribe Wonder levels and bonuses:
Donating resources will improve the level of the Tribe Wonder:
Donating will be made as now, transfering/sending resources.
--- Transfering resources will take time. The time of resources transfer will increase as the level of the Tribe Wonder increases. (to developers calculations)
--- The capacity is limited to the Poloms or Pochteca you select from the city you are sending/donating.
--- My suggested resources needed for the Tribe Wonder would be all four: limestone, obsidian, cacao and corn. ( I understand that corn is not a big issue at lowers levels, but would make sense with the upgrading time part and because workers need food )
--- Upgrading the Tribe Wonder will take time. The time for upgrading will increase as the level increases. ( again at developers latitude and calculations)
Bonuses of the Tribe Wonder:
The Bonuses percentage will increase as the Tribe Wonder level will increase.
--- The current level Bonus and percentage + the percentage of the next Bonus improvement is shown in the Tribe Wonder UI-user interface.
--- The Bonuses for the Tribe Wonder which will be increased alternatively. That means, every level a different Bonus will be increasing (at developers latitude and calculations)
--- My Tribe Bonuses would be: Construction speed, Attack Bonus, HP Bonus, Troops speed, Storage capacity ( The percentages and order of their increase at developers calculations)
My suggestion of Rules and Limitation with Tribe Wonder:
--- Only the Leader of the Tribe can start the time for upgrading the Tribe Wonder.
--- The construction time of the Tribe Wonder is not affected by any construction speed Events.
--- The Bonuses will only apply if the player is in the tribe at the moment of attack or any troops movement. Preventing hit and run type of players and giving time for the tribe to kick players if they feel used only for tribe bonuses.
--- Resources sent over the required amount will be lost. Motivating players to comunicate and plan to prevent losing resources.
I tried to make a preview of the tab in the Tribe UI.
Could be added different image, could be added a story or some other stuff.
Would like to hear your ideas, suggestions and bonuses ideas.
Everything can be changed or have better name, bonuses, rules.