As Surin's building is identical to Buriram's civic building. Then it has elevators at the front and rear entrance. In Buriram the rear entrance is wheel chair friendly and immigration is also on the 3rd floor. We have used it Les.
I remember many years ago when Ms Dow brought her contingent to Buriram (City Hall?) once a month to conduct Immigration matters. Fat Graham (Bronco on ThaiVisa) went and only took his passport, no copies, for an extension. I think there were three flights of stairs to the temporary office. Anyway, he had to descend the stairs and walk about 1 kilometre each way to a copyshop. When he finally returned, completely knackered, the IOs had all buggered off for lunch.