Distance of extra-galactic Classical Cepheids There have been many questions and answers about finding the distance of a star from the earth. But as I did some research on the net, I found that we have specific approaches for finding the distances of different types of stars. 

So, my question is more specific now. 

How to determine how far a Classical Cepheid is?

What if the Cepheid is extra-galactic? Is there a good method to finding the solution?
Can anybody suggest how to make a start at deriving a relation at finding the distance of a Cepheid from us?

There is this Period-Luminosity-Color relation. Can anyone at least enlist the journal articles where I can make a study to get closer to finding the answer to my question?
Since it seems you don't know the equations, I will try to keep it simple.
However, just keep in mind that, in principle, there is no difference between Galactic and extragalactic Cepheids, in this context.

Now, we know that a Period-Luminosity relation holds for the Cepheids:

$P\sim L$

Where $P$ is the pulsation period observed from the Cepheid, and $L$ is the observed luminosity.

We also know that:

$L\sim d$

where $d$ is the distance of the source.

Then it is like to write $P\sim d$.

This means that, if we observe the pulsation period of a Cepheid, we know its distance, and this allows to know the distance of the host galaxy as well.

Some basic sources:

Cepheid variable

Classical Cepheid variable with some numbers

And some diagrams too