well, at first, how big does the world has to be and what kind of biomes dow you want to have in the world?
Also, do you want a continent, landlocked world or a kingdom style with port acces?
Then the world creator has to know what type of trees he needs to use, survival friendly or non survival. Also, big trees or small trees.
At last, Do you want islands?
If you want someone to make a world for you, you need to get these things clear, since the world has to approve to your expectations.
-Alpha
PS,
I'm a world creator, but I don't want to make a world bigger then 7500x7500 blocks.