Place 2 blocks side by side for the base
Put 1 stair block on top facing forward for the seat
Place 1 slab or trapdoor behind the stair for the tank lid
Put 1 lever on the side of the stair for the flush handle
Add 1 button on the wall above or beside the toilet for detail
Use white blocks or quartz for a cleaner toilet look
Place a sign or trapdoor in front if you want a closed front
Add a water source block nearby if you want a bathroom effect