Wooden hidey houses - DIY tips?

Minnie & co. moved into their 2 level 2x4 (currently seperate levels) last week, towards the end of which Minnie was seperated from her three baby boys. I've been pretty determined that most, if not all of their toys and houses will be made from chewable wood, but having given Minnie her own bunny-sized log cabin (that she'll no doubt quickly outgrow) I've realised that these are far too clumpy for a 2x4, especially with providing a neutral space for multiple pigs. The boys have a selection of small cardboard boxes that they chew at. I'd like to make a few of my own wooden houses according to my own ideas of my piggy needs, and wondered if any of you had done the same and had any learnings to share.

Pictures of the new cage soon - we are going to add a ton of cool stuff to it in the next week or so. They are already so happy and do laps at the crack of dawn (their cage is in our bedroom!) and popcorn all over the place. We are probably keeping them all - the thought of four tiny lives depending on me is daunting, but I love each of their little personalities and finding a home that would put me at ease seems so unlikely. I am becoming so tired of annoying well-wishing (?) friends/family who think keeping four pigs (three males in particular) is insane and try to aid rehoming. It is very frustrating to hear people have been asking around "for me". My only response has been - "yeah, if someone can keep two males together in a cage bigger than mine and correctly answer my questions about feeding, call me.". Should work, but how sad it is that I will probably have to explain this madness of mine through their entire lifespans.

Still reading up on these sites and feel like I learn something new every day. Our plans for keeping the pigs are one fixed male kept with Minnie, and two boys together with arrangements changed through adolescence.