My application required only 0.2A to 0.5A and 3 to 8 voltage. I have checked the data sheet of 2N7000, the drain current is around 240mA. Therefore, I am not so sure whether 2n7000 can be used.Welcome to AAC!
The 2N7000 can't handle much current. What output voltage and current are you hoping to get from the converter?
Sorry for left out the design parameter,500mA for 2N7000 → https://www.fairchildsemi.com/datasheets/2N/2N7000.pdf
http://www.simonbramble.co.uk/dc_dc...nverter/sepic_buck_boost_converter_design.htm
http://www.ti.com/product/LM5118/datasheet/detailed_description
non of the parts alone makes your design
but setting limits to- / ranging- your design
may define the conversion frequency that sets requirements for inductors transistors mosfets diodes PCB design e.c.
from scratch it's always possible to make about 2kHz to 8kHz converter with the efficiency of about 60%
if you wan't to get a lot of output current/power your voltage regulation suffers , your efficiency may suffer at low voltage supplies . . .
(as a rule in web forums) not knowing your exact design parameters (web forum rule ends) it's difficult to tell