You need to study the contract carefully. Builders usually have a clause in there to suggest that the state of anything external to the actual property does not have to be completed within any time scales.
I had a similar situation to this recently, where the builder wanted us to complete on a property that had no carpets down on the outside, and the car park was full of building material. When we objected, the builder stated that the outside does not have to be completed, the property itself is finished.
Although that was what their contract stated, we objected and threatened to pull out of the deal and court action to recover the deposit (on the basis that the whole area was inhabitable for a tenant resulting in a loss).
We negotiated hard and tough with them, to the point where they threatened legal against us to complete, but we stuck to our guns and managed to get a few months mortgage payments from them.
Check if the builder is managing to sell the apartments quickly, if not then you have more chance of winning as they need all the sales they can get and will be inclined to negotiate. Of course, check the contract too.
Kess