i was wondering if they made any kind of carpeting kit for the rear part of my car (98 civic EX)

I'm talking about were the back speakers go.
or is this going to be a do it yourself thing.

any hints would be great.( like were would be a good place to get the carpet i need & instilation ideas)

Your talking the shelf where the speakers are. The shelf on sedan/coupe pulls out and the hatches have a simple to remove shelf. Im assuming you got either sedan or coupe. You will need to remove the rear seat backings then remove the shelf cover take the shelf cover and trace it with the new fabric use a contact cement for adhesion. Thats the hard way , if the carpet on the shelf is worn it is a good idea to reapholster it but if its intact and you just dont like the color then why not dye bomb it?
Good place for carpet is a carpet store , fabric at a fabric sewing store. The other way is to buy a new shelf but on hondas and imports small things like that cost an arm and a leg unless you find a wrecked one with very little damage. Lemme know what your full intentions are cus I can help for sure.

i have already taken the back shelf off

so then, should i just make a rough out line and make sure it fits. then touch it up so it looks good

my only problem should be to get the edges to lay flat

it is all metal under it so should i use any sertaint glue or use something els

You can use all sorts of bonding glues for automotive applications try spray adhesives contact cement.

thanks a lot