Depending on which development, getting your own contractor who is NOT one of those "resident contractors" has its fair share of problems... like the example i mentioned whereby one might just cut off your aircon connections while no one is around. Sorry i have no experience yet... but do take your time to select the right contractor... one who is responsible yet "strong" enough to handle harassment from the rest.
Which is why waiting about a year before you start your renovation is a pretty good idea that some Malaysian owners choose to. At least so for the houses in my precinct.
The word 'strong' enough only mean 1 thing. That they pay them behind your back. Which will ultimately come from your own pocket. You will not realise it. But at least your are sure of their standard of delivery as you have already done your due diligence.