Any advice on how, aesthetics’s wise, I should tackle this?
My goal is a 3rd person game, which happens to take place in a zoo. I got the main mechanics out, I just need a zoo.
I was thinking just grid lining it out (Like a New York Zoo)
This doesn’t belong in game design really… But… Just design a map on paper then make it in Blender.
Sorry if I put this in the wrong spot, but I feel like it’s a major part of game design, as it’s what makes the game pop out, you can have no errors or bugs, but looks can make or break a game.
Hes sayin such as, just draw out your design open blender and just recreate your design. You just ned ot know how to use Blender, which I am assuming you don’t. Google has plenty of free tutorials and resources, I personally learned by reading books I purchased at Barnes and Nobles, and Amazon.
You can check out Blender Cookie too. 
I’d advise google sketchup and googles 3d sketchup warehouse(full off free user-created content), and also openstreetmap (if you want to replicate an actual place, however when importing into blender buildings will just become 3d cubes). Turbosquid is also good for free architectural models. But as regards to modelling them in Blender; i’d advise a modular approach, individual models, all lined up together. This will help with animating doors, gates etc. But to design the actual level, get some squared paper, a pencil, a ruler, a rubber and a drink of your choice, go onto google images, get some reference pictures, and map it out in black and white. Then draw a quick 3d image (nothing spectacular) so you can see what you’re aiming to complete.
There’s plenty of tutorials of how to model walls, fences, buildings etc.