Coins

Coins are the most important thing in idle tower builder, as you can upgrade your machines with it and make them faster.

There are several ways of gaining coins: 1. Sell recources at the market and get coins. 2. Revive coins from a free daily gift. 3. Unlocking the cravanserai and sell things and get much more coins then normal. 4th and final way: Unlock the laboratory and upgrade all your bonuses, then restart the building (you got to have coins before you restart the building) then an amount of coins (almost always less unless you upgrade the laboratory to level 999 and thats almost impossible) will remain if you restart the building.

please note that selling things at the market is the best and easiest way there is to get coins. :-)