Complex sentence: Mies was unimpressed by Parkin's concept designs, wondering why one would design a building to be entered through its basement; with this, the Parkin proposal was scrapped, and Allen Lambert was convinced to bring Mies on board.
Split into simpler sentences: Mies was unimpressed by Parkin's concept designs and wondered why one would design a building to be entered through its basement. With this, the Parkin proposal was scrapped and Allen Lambert was convinced to bring Mies on board.