Grey Boxing a level is always a very important early step in the design process. Levels should remain ugly and flexible, but clear and playable while the gameplay is implemented and playtested.

I have done a lot of grey boxing both as a level designer and as an environment modeler. I am comfortable building them both in a 3D Modeling tool (such as 3DS Max) or using the in-engine tools provided by Unity, Unreal, or whatever engine might be used on any particular project.

I can also build and populate a grey boxed level with representative props if such a thing is helpful for the design process.

I understand the need for quick iteration. I am comfortable not getting too attached to a design while I work with the artists, other designers and project leads to ensure the design works for everyone.

During my time at Ion Storm working on Thief and Deus Ex, I was specifically hired to bridge the gap between artist and designer, working on levels that place equal importance on art and design. I enjoyed it very much. And in my time since then I have only developed more of an appreciation and understanding for both disciplines as I have been on both sides of that pipeline.