Is this the Ionesco? The set designs itself! Since the point of the play is the anonymity of individual personality (or something like that -- scholars see it as a precursor to Rhinoceros), the only important detail of the rows of chairs is that they have no individuality at all. Practicality calls for folding chairs, by nature all alike, and because so many are required, no sturdier chairs can be obtained without some sort of accidental difference that the audience would misinterpret in the metalanguage of theatre. As for background, flooring, etc., whatever the stage provides in the raw, undressed, will do just fine. If any distinguishing objects are found on the back wall -- fire extinguishers, pipes -- they can be masked by neutral screens or curtains. Keep in mind Ionesco's philosophical stance in all his stage works (Exit the King continues this penchant for multiples) -- individuality is an illusion.