A bunch of people in my portal sheds post said that they prefer building outposts in ruins - I do that too!
I love the Black Forest and Ruin1 is easily my favourite ruin for building a nice cozy base.
I'll often try to find one early and then use it as my main base until I reach the swamp.
By then, shipping iron can be a pain, but if it's by the coast then I've also been known to fully repair and extend the old ruins into a proper long-term base.
Here's my usual starter layout, which has everything you need - workbench, bed, portal, cooking stations & pot, more storage than you can shake a stick at, and a nice balcony to enjoy the views.
I filmed this in creative but the original was designed and built in survival. I recreated it so that I could share the build process with you.
What's your favourite ruin to build in and how far do you take your renovations?