Help with blending lofted surface with extruded surface

Hello, Im currently in school for architecture and have a project where I am recreating the London City Hall in grasshopper. So far I have made the overall shape and floor structure, but as for the outside shape, I need to create a stepped structure in the back of the building and a smooth continuous surface in the front. Is there a way for me to split and/or blend the two meshes I’ve made to a specific shape? I’ve attached everything, if you open the grasshopper file it is the bottom right purple groups that contain the meshes (they are labled)… please help!! Also sorry for the rats nest that is my layout… still getting the hang of grasshopper
Lofted Front Structure|500x500 (27.9 KB)

You are talking about split/blend, and asking for help. But I do not see the problem here. Specify for what result you are looking for with your current script.