depends what they are obsessive compulsive about. is it germs, numbers, something else...
It would have irregularly shaped windows and furniture, a sloping floor and be painted in green and orange stripes of varying thickness overlaid with crimson trapeziums
it would have peanut shells for flooring, have all the furniture in an assymmetrical pattern and dusted with talc
Visual representations or allegories of the undesirable consequences of contact with or the existence of germs or other harmful substances in the environment --- I'd imagine that would rub them the wrong way.