That's exactly what i'm saying. I checked your city, you have 3 marble factories at level 9 which cost you a total of 1752 marble/2448 planks/2184 steel. A level 9 elvish marble factory produces only 72 marble per day, so you need 24 days just to get the marble back you used to build them, but you built them for the purpose of gaining marble, so it's counter-productive to build them. Your 3 level 10 planks factories produce only 78 planks per day, but you had to use 1976 planks to upgrade them to that level, plus 3304 marble, so you lost a total of 5056 marble and 4424 planks on those factories. You have 5 steel factories, they should produce enough for you trade for the other 2, you could even build a sixth one if you like and trade at a better rating. I see alot of people in my list who keep trading at a 1:1 ratio, 100 steel for 100 marble/planks, but if you trade 150 steel for 100 marble/planks, players who haven't discovered you yet will see the trade as 150:150 (50% trading fee) and will most likely take your trade. Be prepared to take some minor losses, but when you produce alot of boosted goods, those minor losses are still alot better than building non-boosted factories that hardly produce anything and use up alot of precious space.