How to design an LED ceiling lamp
You've got five different design factors, all entangled. 


The heatsink.  That will be a ruling factor in your design. 
The user controls, light switch, dimmer, HomeKit interface, WiFi antenna, and whatever else you care to dream up. 
All the physical parts and aesthetics of the fixture.
The LED emitter itself.
The power supply (driver) which takes line power and makes constant current tailored for that emitter. Any dimming etc. comes in here also. 


I have good news for you: the last two can be purchased "off the shelf" from a variety of vendors from Mouser Electronics to eBay. It's possible you could innovate in this area, but you don't have to.  

The other three are physical crafts, not electronic ones. Well, except for the user controls, where you can go crazy with "Internet of things" type technologies if you wanna.  There's a lot of potential fun in this area, remembering that color LEDs are available.  (their CRI is not as good as decent white LEDs, keep that in mind, so if you're looking for an excellent daily light, you might want to either forget about color, or put two emitters in your light.  Emitters are cheap.