I attempted a king sized bed frame when I’d just started woodworking…it ended in a lot of wasted wood and frustration. It’s a big project and complicated, not so much because the wood working is more difficult than any other project but because the parts you are dealing with are large and awkward.
My advice is as wisconsin bob suggested; find some online plans that you like and go from there. Pine is beautiful but weak, especially when dealing with the weight of a king sized bed. I’d avoid the standard big box store 3/4" pine for the structural pieces…

Rob, Sault Ste. Marie, Ontario