Ok, so give me feedback. Is there any point in keeping this thread going, or does the staff just need to add this to the units and buildings page?
As for David, if you notice when you go into you a city, at the bottom left is a button to switch between producing units and buildings, and buying them. Producing is simply using your hammers per turn to create a units in X amount of turns (dependent on your hammer production). Buying (it might be called purchasing in game, I forget) units and buildings is an instant thing, but costs more gold than it does hammer to produce. For example, looking at my info earlier in the thread, we will compare a monument and a stone works
Monument 40 280 7
Stone Works 75 320 4.27
So the monument costs 40 hammers (on standard speed), and you can instantly buy the monument for 280 gold. This means for every hammer you "buy" or rush if you will, you spend 7 gold. If you look at the stone works it costs 75 hammer and 320 gold. This means you spend 4.27 gold for ever hammer. Speaking simply in terms of efficiency, you are getting more hammers for you gold with a lower number, such as the stone works (4.27 < 7), so if your only goal is to save gold, then the best bet would be the stone works.
That being said, there is a plethora of things to consider besides just the ratio. Maybe you desperately need that culture, or maybe you are about to unlock the Legalism SP and you want to buy a monument so you can get a free ampitheater, etc. For this case, I personally would buy the stone works for the extra production and happiness, and because it is very efficient in gold to hammers, which would then allow me to build a monument quicker; however, as I said, your needs change with every game. This info isn't necessarily to tell you what is the best to buy in any situation, just what is the most efficient to buy purely based on the gold to hammer ratio.