Step 1: Build the foundation
These wooden boards and beams are cut to appropriate lengths and assembled. The target is to get four stable legs and a box where an isolator can be placed and the fire be made. I'm using standard concrete blocks for this. Be careful when making the size of this as it will be more difficult to cut the concrete blocks than the wooden boards (as I noticed).
I've used screws to assemble and hadn't planned on the angled supports but realised they would be needed as it was a bit unstable before they were added. At the top of the four legs I screwed four bolts into the wood, leaving them sticking up a bit. These are meant to be moulded into the concrete top.
Step 2: Making the mould for the concrete top
I went for a square grid and a round hole to place a frying pan. The board was cut into a base sheet and several slivers. These were then placed as the outer rim by being screwed onto the big sheet. For the square a square was screwed together and to give the grid something to be placed onto two slivers were placed lying down, to give it a groove. This was also screwed onto the sheet. For the round hole an old paint can was used which was placed where the hole was supposed to be.
To prevent the concrete to seep between the boards silicone was added along each crack.