If you have ten well-developed cities with no corruption it is time to consider joining the Ikariam elite core of advanced players. Getting eleventh city is moderately difficult, but essentially no different from getting the tenth city. You would need 1.4 million storage capacity that is easily achieved with 3 warehouses in early thirties and 1 dump in early twenties. It is also doable with 2 warehouses in late thirties and a dump in late twenties. It is more efficient to do this with 3 warehouses and a dump.
Getting 11th city is time consuming but easily achievable. Chose what kind of luxury resource your 11th city will be producing on the same basis that marble is good for growth and wine is low maintenance. If you constantly low on wine, make 11th city a wine city, preferably on Hephaestus Forge Island. Your eleventh city needs to have a special layout that sets it apart of all others. This is the first city where you will upgrade the GR to level 10, paving the way for a city number 12. Your 11th city must contain these buildings: 4 warehouses, 1 dump, and the following reducers: sulfur, glass, marble and wood. Wine reducer is not required. Obviously there will be also a Town Hall and a GR. There is now only one free building space left. Some use it for a wine reducer. I use it for a tavern. With a tavern you have a fully functioning city with a bustling population. With a wine reducer you get a shell of a city that is almost vacant of inhabitants. The extra inhabitants will produce more wine than the wine reducer will save, plus there will be a veritable gold income from that city.
My eleventh city is wine. If you have trouble buying sulphur you may wish to get a second sulphur town.
Building twelfth city is hard. It is probably the Ultimate Ikariam challenge. It can take anything up to a year to get the 12th city. While building tenth and eleventh cities was essentially achieved through the tedium of upgrading storage capacity and gathering recourses, building 12 city will involve demolition of several buildings that will temporarily wreck a city. For 12th city you need 4 level 40 warehouses and a level 40 dump. These buildings will take a lot of resources and time. But late in the game there is not much else to do, but build, build, build. If you get tired of building you can always switch your attention to alliance wars for a while. Eventually though your 11th city will have 4 level 40 warehouses, level 40 dump and level 10 GR. Demolish sulphur reducer and build a museum (or an academy, if the next town where you intend to upgrade the GR contains academy that you would need to demolish). Your account is among the top 100 in the server. Rejoice! But that is not the end of it. You now have 10 more cities to upgrade. Upgrade them one at a time. These stonemasons and foresters will have to go. You would need building slots for 4 warehouses and sulphur and glass reducers. Glass reducer though is optional.
If you have to demolish a high level museum to get a spot for a glass reducer you may reconsider – look at the amount of marble, wood and time invested into the museum, consider the population drop and loss of income too and compare this to the amount of glass you would potentially save. If you have only a low level museum and glass is hard to come by, then go for it – wreck your museum. This is why in my earlier tutorial I advised to get museum to no more than level 12. So enjoy the game, upgrade those warehouses to level 40 wherever you can. Upgrade GR from 9 to 10 only in one city at a time. If you are becoming disillusioned with all these incessant building upgrades consider becoming a major military power. Read our Ikariam War guide.