I noticed that once we use a golem scheme to create the golem, the scheme dissapears from the crafts option list. Do we need to use another scheme of the same golem to create another or does the scheme reappear after the golem lifespan is over?

Example, I have one cottom golem with 9 days left. I have another scheme in my inventory. Do I need to use this new cottom scheme to create another cotton golem? If so, do I have to create it after the other one is out of days or can I have two cotton golems producing cotton at once?

The scheme reappears in your list after the golem dies. Even if you try to use the 2nd scheme, the game won't let you - There's no way of having two of the same golem at the same time.

Ok thank you for explaining that, I'll try to trade the extra ones then :)