This is a static model with room for electronics, it is the same size as this movable tracking model from which also contains instructions on how to make the legs: http://www.instructables.com/id/Building-a-moving-and-tracking-Portal-Turret/
I made it from screen shots from in the game and some things are optimized or removed to be printable.
There are extra parts for the guns that have been made with extra clearance, and the split ammo box for gluing to the shell.
The shell, dividers and the side panels have holes for 1.75mm filament as locating pins.
The parts are not oriented into the optimal orientation for printing but all have a flat face to be printed from. I recommend printing the guns with the barrels pointing up and it gave me a nice result.
Many parts require supports as you can only optimize so much before taking away too much and altering the look too much, only two wires on the middle part were removed and the bottom part was redesigned to fit the legs from the moving turret design.
The legs require 3mm aluminium sheet metal and 4mm stainless steel rods, the guns and side panels are supported by an 115mm long aluminium tube 8mm in diameter.
There is plenty of space to put electronics inside and in the gun barrels you can put 5mm LEDs. The part bottom 2 has a hole for powering any electronics you put inside, but I have not printed it.
Re-orient the parts for best result.