Because the instructions to build this bed are essentially the same as the plans for the Queen sized (including the bed frame), I will just be providing diagrams on how to build the Heaboard and Footboard in the king size.
Please review the plans for the Queen Sized with Arch and the Queen Sized Farmhouse Bed plans before begining this project. Follow the plans for the Queen Size with Arch for building the side rails, if you do not have a metal bed frame. The length of this bed is identical (80″) to a queen size. If you do not have a box spring, you can use slats. Please review the post on the Twin Sized Farmhouse Bed here. There is lots of information here – look at the comments on how to add slats to the frame. The slats will be 80″ long, I would space them closer or use bigger boards, like 2x4s.
Please also take note that King beds vary in size depending on where you live. You should always measure your mattress first and make sure that it fits the bed. There are also California King bed plans available. The measurements given are recommended for a bed 80" wide. If your bed is narrower, simply trim off from the panel and panel trim boards, or substitute 1x6s for the end boards in the panel.
Also note that when you build with standard dimensional lumber, widths can vary greatly depending on where your lumber was milled. Always measure the width of your boards first. This plan assumes that your 1x8s are 7 1/2" wide - the widest possible measurement. Check yours, adjust accordingly.