First, put down two wooden planks back to back then place a chest on the back one (Whichever one you choose to be the back one). Then crouch and place a wood slab on the front of the chest (Top half recommended).
Then place a trapdoor on the front of the wood slab and make sure it closes right. Then just put walls around of whatever. But DO NOT PLACE A FULL BLOCK ON TOP OF CHEST OR ELSE IT WONT OPEN. Only place a slab on top of it then it will still work. Then you’re done!