Between three areas of my old home (100 years) there are three different ceiling heights. The second story has no variation on the floor. They are all drywall ceilings (with that really ugly textured paint which in the kitchen is chipping off). Is it most likely that they were trying to cover up the old plaster ceilings and didn't bother to use the same technique each time. Between the three ares there is probably a 3 or 4 inch difference. Any thoughts would be appreciated. Thanks

What are you trying to do? Replace the ceilings?

If so there the options are many, drop ceiling, those 12X12 tiles that you staple to furring strips. You could drywall over the old drywall and finish so its smooth, you could apply a new texture over the old... the list goes on and on..