Outside view: The door is open because it's bade of Redwood bark, which is described as "camouflaged", meaning mobs don't see it as a door. No midnight knocking here.
Ground floor view... Just the bare necessities. I hollow out 3 blocks high, and also remove extra bark on each side of the long walls. This gets me about 2 1/2 stacks of redwood and 26 barks, including the doorway. I usually half-slab the ceiling to keep Endermen away on rainy nights
I built my basement at level 50, hollowing around the roots to create an antechamber. I have room for a couple of floors between here and ground level if needed. I can also build up from Ground if I need extra room or wood. You can see the Smeltery straight ahead. There's a garden to the left, storage to the right. My mining hall is to the rear.
Garden
Storage
Left side of mining hall. Openings under torches are for stairway shafts.
Right side of hall. The opening at the far end on the right was for a Turtle quarry, until I found that Turtles aren't in Unstable (yet)