DIY Protein skimmer?

[pike]

I am going to attempt to build a protein skimmer for my 125gal reef. This tank will also have a 30gal sump and a 30 [acronym:22083e88bb="Gallon"]gal[/acronym:22083e88bb] fuge. Just because I have two 30gal tanks from an old [acronym:22083e88bb="Freshwater"]FW[/acronym:22083e88bb] project. So with all filters, and tanks full I will be pushing around 200gal of saltwater.
Is this how I should look at it? Or should I just consider the 125gal for the skimmer?
What I really want to know is how big should I make this skimmer. I understand the taller I make it the more contact time the water and micro bubbles will have. I will make a venturi style if at all possible.
I am thinking about going with 4"-5" [acronym:22083e88bb="Plastic pipe"]PVC[/acronym:22083e88bb] with a 3" reaction chamber inside. Or maybe a 5" Sq. plexiglass box. Anyone have any pros or cons on going with a sq unit opposed to a round one. I know the drilling, and the application of bulkheads will be EZer with a sq box unit.
If the micro bubbles exiting the skimmer wont be an issue because of other filtration occurring after the skimmer will I need to use a reaction chamber? How I understand it, the two separate chambers are for the reduction of micro bubbles exiting the skimmer and entering the main tank.
I have looked at many designs from others that have built these [acronym:22083e88bb="Do it yourself"]DIY[/acronym:22083e88bb] skimmers, but none I have seen tell what size the skimmer is rated for.
Has anyone ever built one and what are the specs for something that will skim around 200gals.
Thanks!