creating item based on custom folder content type programmatically

Dears,

How can I create an item based on a custom folder content type programmatically?

ex: I do have a folder content type with following fields :

1.Title

1.Purchase Id

Once I create an item with the above content type, I will insert more documents inside the folder. 

how can I perform the above steps programmatically using a web part? 

thanks in advance,

Ammar