Ah, but you can't get out if you're not inside in the first place, now can you?
maybe if you define inside and outside to be the same, or to be non exclusive properties (like a set, which is both open and closed)
There are two ways to get to the solution for this problem. One, a building made out of "cement" would have no strength and would nearly crumble under its own weight if you could even get it to form walls and a ceiling in the first place. So you could just knock the walls down bare handed and walk out. A concrete building on the other hand would be very strong. So this is a trick question. Two, if the interviewer really meant concrete then he is probably in HR and won't understand any answer you give anyway. But playing along, since you are not "in" the building now, you would have to ask how you were placed in such a circumstance...if there's no way out, how did "they" get you in? If you are dead and the building is a tomb (and built up around you), then there would be no point in getting out. For either scenario, I don't think I would want to work for this company, and the real solution is to end the interview.
Or there could be a doorway, but no door.
No one said anything about a ceiling. I would just climb over the wall.
Even easier: If there is no ceiling, topologically, you are already outside.
Actually the answer is Smale's paradox.
Assuming we are living in R^3, we compactify R^3 to get S^3. Then the "intuitive" inside and the "intuitive" outside have honestly no difference.
"You are in a cement room with no door and no windows."
A true mathematician would explain how this statement is false.