Refer to majlis if u want to have approval for your building / house (MBSA / MBPJ / DBKL etc)..
Normally they have specific design and sometime you will dislike it..

Get quote from several contractors..if agree, then engage them..

Manage ur contractors..u have to frequently pay visit to the progress..because we are working with human here..

Having approval from majlis will eventually increase ur house valuation.
Valuers value ur house based on approval.

For fast and easy approval by majlis, they will suggest their design..

if you're going for your own design, you must ensure / engage / hire a reliable consultant / engineers / architects and etc which know majlis standards / law / restriction and etc..
Otherwise, might involve lots of design change and etc..which is not free..prepare for panadol actifast!