It might be a bit late to make this post, but there are already a number of private and semiprivate organizations that provide non binding codes for various things.  W3C for web standards, Underwriters Laboratories for all kinds of stuff, in Germany TUV (with dots over the U sorry, on a US keyboard) started as a  private organization to make steam engines safer (though I'm not sure how it's run now), FAA doesn't regulate skydiving dropzones, but there are rules set up by the amateur organizations.   There is no reason to believe that buildings would be any different, it is almost certain the building codes did save some lives, since without coercion there would be less than 100% compliance with any code, but if I want to build a building that is going to fall down, and it won't damage the neighbors buildings when it does, I should have the right to do that.  Obviously telling tenants that it is up to some earthquake code, then knowingly constructing to lower standards would be fraud, and very few libertarians would say that is ok.  As for the more complex issue, of say, skyscrapers that cannot collapse without significant damage and loss of life on neighboring properties, I don't really see much way around regulation there.