What would be the best way to create an exterior for this model?

JoJa15

I am fairly new to 3D modelling and this forum. I have an elevator car that someone else modeled that I would like to create an exterior for. I have created other 3D models but they were solid objects with no interiors like a helicopter. For some reason I struggle with creating an exterior for an object that already has an interior or vice versa creating an interior for an object that already has a solid exterior.

Here is the elevator car that I am working with:

I would like to be able to create an exterior for the car so that players could ride on the outside, and view it from all sides.

Here is another example of a building that I have that I would like to create an interior for:

I am going for a low poly art style and I am using Maya. 

I would appreciate any advice, tips, tricks, or techniques on creating an exterior for an interior model or vice versa creating an interior for an exterior model. Thank you in advance for any help provided!

JoJa15

I figured this out on the elevator shaft. I took the edges on the outer front opening and extruded them to create a front face. Then I extruded the outer edges of that front face backwards to create the sides of the shell. Lastly I used Mays fill hole to fill in the back.

Brian "Panda" Choi

What architectural style inspire you the most?