How long did the pyramid take to be build?

Around twenty years

Explanation:

In my old history book, it says "Herodotus was told by his Egyptian guides that it took 20 for a force of 100,000 oppressed slaves to build the pyramid (with another 10 years to build a stone causeway that connected it to a temple in the valley below)."

So, for the average pyramid it would take 20 years (give or take depending on things like weather, the slaves building it, etc)