In real life it is not a percentage as it is not linear. When you increase span, the needed height of a slab or beam increases faster than the span.
I live in a harsh climate so here insulation determines the thickness of exterior walls. As a rule of thumb I use 400 mm for a frame wall and 500 mm for a concrete or brick wall. Interior walls can be anything from about 100 mm to 200 mm, the latter for a load-bearing concrete wall. For floor slabs, prestressed concrete allows something like 8-9 meters for a 300 mm slab. For wood framing, the same thickness would probably be enough for normal spans in dwellings. Insulated framed roofs need a thickness of 600-700 mm.