How do you make a modern duvet cover for king-sized bed?

I sewed to flat sheets together. You have to search a bit for a place that sells the sheets separately but I was able to do that. If I remember correctly, queen sized flat sheets worked for me but you would have to check the dimensions. You can always tie-dye or embellish the sheets however you want. I sewed 3 sides together then made buttons holes and sewed buttons at the bottom where the opening is to slide the comforter in.

i dont use top sheets so i sewed them together 3 sides and slid the comforter in used snaps to close it

Thank you. Good idea.

the sheets work great. After I am finished with the sheets ( I change colors a lot) I cut into a continuous strip a using Q size hook, crochet rugs.

2 sheets sewn together..add tassels for a little more pizzazz!

I make lots of these for disabled clients, I do the same as the ladies above but I use a long upholstry zipper to close mine. And I sew ties inside corners of duvet cover, and sew loops on comforter to tie them in place. When I sew the sheets together I first sew them right sides together on 3 sides, then turn and press, and then I sew a border all the way around..... usually 1 1/2" to 3" to make it look more finished. When I select the sheets I pick two colors so they can be flipped.

To decorate them if solid colors, I have put an applique in the center, I have used fabric paint and a stencil of a quote.

If you want it puffy, I have lined the inside with quilting fiber, then sew little fine satin ribbon bows.

I did one ladies bedroom all in deco lace, where I shopped thrift stores for cotton table cloths with interesting deco designs, then I made curtains and applied two of the table clothes to her duvet top after using diluted fabric paint to lightly color the center design with yellow and green. Must say it was one of the cheerist bedrooms I've ever done. I painted a high-boy chest of draws yellow, laid a piece of lace over it on the ground, and spray painted it white so the lace design was on the wood.