Id like to make bootable ISO of a directory using mkisofs + grub2.

so

What have you done so far ?
where exactly are you stuck ?
what have you already done ?

I don't know much about those files, but you should be able to right-click on the folder, hover over "Actions", and click "Create file project with K3b" as long as you have K3b.

At least, this works for me. You will need a CD-R/CD-RW writer and a blank cd.

I think the OP has a file directory/tree of everything a system might have starting at the / directory, and wants to turn this into a bootable ISO to fire up that system. Or maybe he just has data in a directory and wants a bootable system added and made into an ISO that can let him have is data on the ISO (or CD or DVD that gets burned from that).

So we are talking setting up a system that can understand how to run from read-only media (e.g. does not need to write over itself, but writes in RAM instead), and a bootloader to make it go (GRUB being his choice, though I'd go with ISOLINUX).