What do I need to build LED bulb
This can be such a general question that it really depends on what problem/challenge you are trying to solve.  How much light do you need and how wide of an angle of distribution do you need?  I purchased many thousands of OSRAM TopLED plus (warm white) SMD LEDs for little over 4 cents each.  In an array you can generate a reasonable amount of light with only the PC board dissipating heat.  If you want higher levels of light you typically need a heat sink and a way to manage the current draw from the LEDs.  Now that I can buy a 75 watt equivalent flood lamp bulb from Feit Electric for ~$20, I do not try to build large LED bulbs since it would cost me as much or more to produce them.