It is really simple to build one and difficult to go wrong although you can go wrong. Ours could have been just a tad wider but it fits nicely behind the atv. The landscape timbers were 2 that a neighbor threw away. The cross pieces were some old 2 x 6 pieces I had in the barn. I did buy bolts but they should have been just a tad longer (sticking up 2" is nice). I like to leave them long, sticking up. In this way they will bite on the log as you are rolling it onto the dray and proves to be a big help. Eyebolts on the sides to have something to strap down the load. A chain on the front to pull. A friend (see the last 2 pictures) built a couple drays after asking how I did ours and he made his so it could be pulled from front or rear which is a great idea (The runners would have to be slanted on both ends). If I build another, I may do the same thing. Bob built 2 drays (pictures below). The first one did not hold together. He sunk the 2 x 6 into the runners which weakened the runners and they broke. So the next one he did not sink them and it works great. He also built his larger than ours but the nice thing is you can build it to pretty much any size you want. Someone asked me about having 2 tiedowns but I do not think you would find that necessary for hauling logs. But if you hauled other things on the dray, which you can, you might find an extra tie down handy but it could easily be added at any time. Bob also put a longer chain on for pulling. I like a shorter chain though especially if pulling in tight quarters.
Thanks for the detailed look at your dray. I am guessing you are using stove bolts, the ones that have rounded heads and don't stick up much. How heavy duty is the chain you put on?
Did not use stove bolts; just counter-sunk the heads on the bottom of the runners. Don't know what grade that chain is but it is a lot heavier than necessary. For this size dray you don't need a very heavy chain at all. I think Bob used 3/8" but 5/16" should do just fine. Unless one is hauling, say, a half dozen logs 36" diameter and up with length of 12', there is not too much to worry about with strength of chain.