Hi,
there are many ways to connect a FET to an amplifier.
* N-Ch, P-Ch
* as voltage follower
* as current source
* and so on
--> show your schematic. If you did not draw yet, then it´s high time, at least for a sketch.
***
A design starts with requirements and specifications. Then to find a suitable solution. There are plenty of LDO designs around. Many come with design notes, examples, calculations...
Just do an internet search, read through a couple of them. Choos the document that suits you most.Try/calculate/simulate on your own. And on questions, show what you have done so far and refer to the document you used.
Klaus