FAS2552 with 12 X 1.2 TB Disk.. using ADP to maximize the disk space.
you can space them two different way.
I just run this using netapp-sysnergy and here is the screenshot of the reports.
FAS2552 with 12 X 1.2TB HDD

Option : 1
While you create 1 Root aggr and 1 Data aggr on Each node. (to maximize the CPU Usage)

As you can see the above configuration give you exactly the same amount of space on each node.. but it lost 2 parity disk and 1 spare on each node.. So total you lost 6 disk worth of space. (which is almost half of what you have, and may not be ideal for your case)
Option : 2
Create root aggr for both node..
But use the renamining disks to create one large aggr on one of the node. (7.69TB total usable space)
Advantages :-
Aggr is larger.
Disadvantages:-
You are not using most part of the CPU resources on node-2

If you don't need all the CPU resources the 2nd node can provide, you may choose the Option-2
I know few of customers choose this option after considering their Storage Resources usage.
hope this help
thanks,
Robin.