I have implimented a 3 Stage Ring Oscillator using CMOS here. I researched my initial circuit in Wikipidia Ring Oscillators.
I also read up on some books and research journals on how to implement my design and finalized my model.

Steps taken by me while designing the circuit:
1. I designed the circuit using eSim simulation software and after that I generated the netlist for my circuit.
2. Then I replaced the CMOS componets in the netlist with the models of Sky130 and defined the parameters.
3. I ran the completed the netlist using ngSpice and got the desired output waveform.

Problems I faced:
1. I initially ran into some errors while running the netlist using ngSpice but I resolved it after some debugging.
2. I also faced problem while replacing the eSim component models with that of Sky130 as the Sky130 model's specifications 
were not clear on the surface level so I did not know which model to use.