I started a couple years ago making terrain for a Dungeons and Dragons campaign before my imagination spread out into the vast world of 1:12 scale miniatures.
I'm not a stickler for exactness. If it's kind of sort of the right shape or size, I'll stick it in my scene. I use anything from pink house insulation foam to straws, coffee stir sticks, and chipboard.
As my mood varies, so do the rooms I create - one Christmas I was feeling the season and created a scene from Charles Dickens' Christmas Carol. I do prefer to create messy scenes involving lots of books. Even in sparse dungeons, I'll hide books. Witches, wizards, potions, spell books, apocalyptic scenes - these are my bread and butter.
Some projects take a couple of days, but the more detailed ones can take up to a month to complete. Somewhere along the way, I started teaching myself graphic design so that I could create printable things to put in my scenes. Spell pages, book covers and cabinet photographs (of my own ancestors!)
More info: Etsy
#1 Nevermore Books (A Fantasy Themed Bookstore)
#2 The Wizards Library
#3 Aldraths Academy, A Wizards Office
#4 13 Acorn Lane
#5 Scrooges Counting House (A Christmas Carol)
#7 First Edition Books
#8 80's Punk Bedroom
#9 The Detectives Office (A Detective Going Through A Rough Time)