For us typical design fees for your house size is about Rm4/sqft.
However I strongly recommend to appoint ID for design and build to ease your coordination job and also generally smoother and better quality project compared to those owner that only appoint ID for design and build their own with own contractor .
Because ID normally more experience with the renovation sequence,types of material, all the many small details of the design that need to pay more concentration when build to prevent problem or lousy quality work.

Of course you need to get a good and responsible ID that will make sure your home is in the safe hands.

Happy renovating !