3D Computer Game Engines - Basic Blockout

Following from the work within my previous unit, the work for which can be see here, I began piecing together a basic blockout using template floor and wall panels provided within UE4.
I was initially going to import my ground floor map layout and utilise it as a texture within a material, placed on a layout block for accuracy, but having done this with other work and the scale not necessarily working out as expected, I have decided to go without a the top down plan and work on it sheerly from reference, building freely within the Unreal Tournament 4 editor.

Using differently sized cubes placed, at this point, randomly in sequence, I have produced a ground floor with a base level of obstacles which are to be navigated around, and can also be used to take cover.
The longer term plan for these cubes is to be replaced by individual sets of meshes incorporating pipes and metal panels to hopefully represent the intended steel mill type environment.
I will be trying to implement tunnelled sections of piping also, which players will be able to navigate through, for example, below is a UT4 Character pawn sized cube in Maya, with half of a potential pipe tunnel, made from an easily varied pipe radius.

I have also placed a long, thin rectangular cube across the central area of the map, in place of the environmental trap I am hoping to configure in the map.

My base blockout can be seen below.

I will be continuing with this blockout process, and adding either a second floor as necessary, or a set of walkways which are elevated above the environmental hazard for navigational ease when the hazard is active.

I may make both walkways and a second flood provided it doesn't take too much time, as the second floor could be used within an alternate game type, Team DeathMatch for example. This will allow me not only to playtest both layout options and judge on which method would work better but also to receive peer opinions based on the layout throughout the process.