How can I start writing a Matlab code for making LDPC code?

From where to start to writ any Matlab code for LDPC encoder / decoder? I want to use this LDPC code for part of another project.

I need to make a LDPC as follows:

1. create H matrix with different rate(but at the time i use one rate)[most of the available code on the internet is for rate 1/2].
2. length of the code words is variable and depends to the which situation program in is changing.
3. encoder function
4. decoder function.

Any suggestion? Any good code or tutorial? Any references or link? or any simple code to explain about LDPC with simple implementation