>>64093559Depends on the size, if you want it real big you should buy a mini excavator, if you think you can so it by hand do it.
Determine frost depth, this is the depth to which the ground freezes every year, if the foot of your bunker is below that, good, frozen ground will lift buildings if they dont sit underneat it and tear off waterlines etc.
Do a layer of gravel all around then pour like 1cm of concrete and roughly even it out. On this you can place the coverage to hold in place the concrete for your real footing, for rebar just ask the guy at the store for sonething that always works, you cant do too much rebar. Important, have one mat on the ground and one at the top with a few cm back from the exterior layers. Then buy precast concrete bricks and build the walls, then get some picrels adjust to height, layout the boards for coversge and cast the concrete like you did before, rebar is alot more important here, just ask the guy at the store. Now you look at a youtube video on simple timber framing and build the cabin, then you do another layer of concrete without rebar on a layer of insulation ontop of the bunker ceiling on which yiu can layout the floorboards. Now plaster the thick bitumen stuff around the outside of the bunker walls, glue on installation, fill the hole with gravel and then plqnt some nice flowers in your gsrden