Myself if the cost was equal, I would build. I enjoy not just the building of terrain but the whole process, Planning, drawing it out on paper, getting the materials, the building of it, and finishing it with painting and the finial touches. For myself I find it relaxing and my mind not thinking of the day's events.
I just discovered sculpting and now I have a whole list of figures I would like to do. Again the whole process likrmthe terrain building is relaxing for me.
Plus I like to make the stuff that I am sure I may not be able to buy commercially that fits in to my different worlds to which they fit in. I like 15mm scale and there is just not enough terrain in scale for my liking, Sci-fi, Pirates, Pulp, Zombies and Post Apocalyptic.
Well there's my two cents.