Making a 27 cell iron farm... prepare to work straight for 2 weeks
Ender man and iron farms are two different beasts. One for xp and one for money
It only took me a few days or so to get mine running.
Although I s'pose I am still making modifications here and there to make sure it is at max-rate. And I did spend most of my waking hours working on it and bought materials instead of farming them.
But yeah, it would be much easier for you to make an enderman farm than an iron farm.
Although, 1 tip I would give you if making an iron farm: Always have at least 1 cell working primarily on breeding villages to populate other cells. When I did mine, I put the villagers on the interior of my central cell and transported them from there. When I was on the top layer I moved them to the top of that layer. Makes it easier to populate the cells instead of having the village be completely external.