Hi CC
We have just had this done! Awaiting the builders arrival on sunday to finish the last few outstanding issues. You are very welcome to have a look. We're close to springs. I can give you a rough guide to costs but our extension was mixed in with lots of other work. We are really pleased with the extra space and getting permission from Emaar was relatively straight forward.
Also, I noticed that you replied to my salesforce.com thread, shall I post my email address so that we can have a quick chat?
Thanks
You need permission to make any alteration to any property from the developer.
For Emaar the details are here. http://www.emaar.com/index.aspx?page=faqs-householdservices
I believe you need to pay a deposit which is refunded once they have inspected the work & ensured it is completed to their satisfaction, you will also need to submit drawings etc.