A 4x8 space is rather small if you're wanting room to move around, i'd recommend looking into a single 4x8 tent or two 4x4 tents instead of building the room as it would make things much easier for you. The tents can be placed strategically so that they provide easy access to the zippers on the side. This way you can open up any part of the tent and peek inside.
Another thing to consider is that a 600w light is most efficient in a 3x3 space, if you want to fill a 4x4 space I recommend a 1000w light. I mean, you can fill a 4x4 with a 600w but the buds won't get as dense as if they were in a 3x3 space. Plant needs a minimum of 50w per sqft. 600w/9sqft = ~67w/sqft where as 600w/16sqft is 37.5w/sqft.
If you're set on building the room though, absolutely make it a 4x10 instead of 4x8. You could have a single 3x3 on the left, and another on the right. This would leave you with 6ft of space to work with, since you only really need 4 you can leave the 3x3 screens a foot away from the wall so that the buds don't start hitting the walls.
I'm doing something similar to you, although I do wish I had more room to work with I'm able to do all I need. Carefully plan and consider every aspect of your grow when designing your plans so you can determine the most effective way to do things.