Allow easy change of category and take their characteristics, like make openings and add doors/windows on it in case of a wall and let it join to other walls. You already allow attaching walls into imported roofs and floors. Allow dividing surface of masses and adding adaptive components on it(we used to be able to do this (why would you take such an amazing feature away? please bring it back). Allow assigning materials easily right from the properties toolbar to each layer imported.