Deanna: These may help you
Is it an existing closet or (as I'm assuming) one you are building? If you working in the corner of a room, you already have two walls. When you build them, you have a 2x4 at the bottom of what is basically a partition wall, an opening for your door, a 2x4 at the top, and the framing in between, plus your side wall. The more you plan for depth and width, the better your closet will work for you. Do you want a walk in closet or one you reach into? Plan your doorway accordingly so you can reach all of the closet. Try to stick with standard measurements so you don't have to custom order or build anything to fit.
This tutorial may be helpful https://www.hometalk.com/3703640/slanted-wall-built-in-s-with-hidden-storage
It shows how to build a unit that can be used as a closet withe shelves and hanging space.
This may help https://www.familyhandyman.com/closet/how-to-build-a-wall-to-wall-closet/
Hi Deanna, here's a lovely video that will help - https://www.youtube.com/watch?v=xEDeM6l_HbI
Standards for your planning:
Depth: 24” clear.
Closet Rod support framing: 12” deep.
Studs in corners & 16” on center.
You can build it on the floor and then tip up the wall panels.
Or “stick build” it.
Hi, To answer you question -
I assume you already have a closet, and just want it to look better where it meets the ceiling and surrounds? If that is the case you can use Architrave or other molding available from the DIY store. If you ask someone, they will help you find the things you require to do the job! Best wishes.