At the risk of seeming pedantic, I'll point out that (unless you're planning on inviting guests to stay overnight) what you want isn't actually a bunk bed (which has two beds, one above the other) but a cabin bed (which has a bed above a space which can be used as a desk area or for storage purposes).
While these images show kids' beds, they're good enough to illustrate what I mean:
https://www.noaandnani.co.uk/images/high-sleeper-cabin-bed-in-white-thomas-p287-1759_image.jpg
https://secure.img1-fg.wfcdn.com/im/37332210/resize-h800%5Ecompr-r85/3795/37951075/Frankie+Cabin+Bed+with+Storage+and+Desk.jpg
It's worth noting though that our transatlantic cousins tend to refer to them as 'loft beds', so if you're googling for plans, that's an additional search term to use. (Annoyingly, 'cabin bed' seems to mean a bed built to look like a wood cabin to Americans, so there are loads of false leads when googling that term).
Searching for 'DIY full size loft bed' on Youtube brings up several possibilities, including one which links back to this page:
http://jayscustomcreations.com/2013/03/full-size-loft-bed/
I probably won't have solved your problem but I hope that I might have given you a few pointers as to what to look for.
Happy hunting!