Cube

[kube]

I want to make a 12 x 12 x 12 cube and attach it to my 20 long sump that i currently have. How hard would this be to make? I was thinking I could try to make it out of thick plexi glass.
Is the 12 x 12 foot print large enough to house most nice skimmers out on the market for 125 gallon tank?
I was thinking two 1in bulk heads to attach it to the 20 gallon tank. Also since this would be attached to the first chamber in my 20 long that has a baffle at ten inches this add on would always be at ten inches correct?
Any good links to how to make this? any suggestions of flaws in my logic here?

 

[kube]

or would it just be easier to add a rubbermaid tub w/ a couple of bulkheads?
getting estimates from glass cages