[Question] Envoironment creation pipeline

Starkist

Hi folks,

I have a question about environment creation approach.
I need to recreate this map:

I wonder how should I approach the block creation, should I create then as they are in chunks / boxes? or create walls and floors and construct then together? 
The game is topdown, this is approximately the camera angle:

I hope you guys can give me some advice, perhaps some pros and cons for whatever approach.

Thanks ahead,
Michael.