1)First of all you have to go through tranmission gate concept and how it gets its structure from nmos and pmos.
2)Than 2x1 mux internal structure concept is to be followed that how it i formed by using two trabsmission gates.
3)Than select line as well as select line complement is needed for mux o an inverter is required which can be using a cmos inverter.
4)Connecting all this systematically with refernce to the 2x1 mux you can get the 2x1 mux by drawing schematic in esim and generating its netlist.
5)I faced many challenge like:-
	a)you should know how to make transmission gate from nmos and pmos.
	b)you should handle bulk terminal of mos correctly in Tg gate as well asin cmos inverter.
	c)you should take care of vdd and input voltage for getting correct waveform.
	d)mosfet sizing and delays should be handeled properly.
	
 
 
