Even if your character comes from a nomadic or subterranean culture, they probably still slept in some kind of shelter as a child. Homes come in many different variations, some more lavishly comfortable than others. But that comfortability factor is entirely in the eye of the Beholder (pun intended) and only your character can determine that comfortability.
Start out by describing the structure where your character grew up as a child. How many rooms/caverns did it have? Was it damp and stale (cave)? Or did it smell of perfumes and have decorative tapestries on the walls (palace)? Did your character feel safe and secure in this home (castle)? Or was there a constant fear of being attacked by predators or enemies from another group (treehouse)?
Who lived in this shelter with your character? Parents? Siblings? Extended family? Fellow orphans? Guards and staff? Was there enough room for everyone, or did you all have to crowd in there for warmth or safety?
How did you character feel about this home? Did they enjoy living there? Or did they dream of something bigger and better?
Childhood homes can appear in many shapes and sizes. But the real question is, was it simply a "house" where your character could take shelter from the storms and turmoils that the physical world might throw at them? Or was it a "home" where they could take shelter from the storms and turmoils that life might throw at them. Only your character, and you the player, will be able to determine the differences between a "house" and a "home."