Then, you have no case.

Then, you have no case, unless you can prove that the seller cheated you into signing the walk-through agreement. With your signature on the walk-through agreement, the condo is deemed acceptable by the buyer, you. Did you attach any conditions in writing to the walk-through agreement? Oral promises are nice and the builders generally would eventually keep up with their promises, but SLOWLY. What you are dealing now is after-sale customer services.
If there are many complaints against the builder, there is a chance of class law suit. Well, class law suit seldom gets the victims anything real.