@Olim-Nagev It's funny you mention that challenge because I have done that, although it was only with computers in a single player game. Doing it in an online automatch would certainly raise the bar. Therefore I will add it to the list!
So, from that PDF: Page 7. City Improvements. (right hand column)
"The first improvement in each area always costs 1 commodity of the matching type. The second improvement in each area costs 2 of that commodity. The cost of each subsequent improvement is again increased by 1. "
So, to elaborate, the first city improvement costs 1 commodity. The second 2; third 3; etc. If you have more of the correct and matching commodity (and a city, as stated further in the rules) then you can do as many improvements as you can afford per turn. Example: if I have 6 paper, I can make the first, second and third city improvements for "instants" aquaduct.
I would love to jump over the lower improvements and get a metropolis right away, but alas, we have to pay for it. I hope that helps.
Man I was excited to get my friend playing this game with me and we had fun for a few games but tonight it was brown screens with no game starting. I couldn't even play him, you probably would have have another purchase . Then the rest of the night I have been unable to even play 30 secs of a match, switches to me, and kicks me out of the game faster than the turn timer is supposed to be and says I had no net connection. My motel net is so crap and this is the only game I can even play. Keep auto losing so lame.