Questions - Need some input

I am ready to make my sump, i am getting my 20 gal long tonight. can someone tell where to find the sizes for the dividing pieces , how many, what depth to set them,Is there a blue print somewhere i can get.

I really could use some help. this may be long also sorry.
I just got my sump on Tues, thats the good part I hope. here is what I think is my problem. 1 will not fit under cabinet unless I take tank apart and start over. 2 is there ever a time when I will have to take sump out from under the tank. 3 should I wait until I get my skimmer then do everything at once. 4 here are the numbers to help with next question,
sump dim are H 16" L 24 " it is divided by one single partation, ...