Help on Creating Undulating Surface with Controlled Points

From the beginning I am aiming at creating a model of my project, its similar to Peter Eisenman's City of Culture in Galicia. I bet this has been done so many times. Its simply trying to create undulating surface, before I finally trim it according to the context of my project. I hope I'm going in the right direction. This time I just created grids, select some points from the data tree and split them from the main. But then since I still suck at handling data tree, the output where I tried to create the surface with surface from points is a big a mess. I tried delauney and patch, but it doesn't have the look that i'm looking for, and with the surface from points component, I could toggle the interpolation.

One issue is that the U value of the surface from points component is weird, I can never get it right (that's why I put the slider there, tried to find out what's going on).  I think the mess is caused by the splitting, where I am trying to first split the main data to find some points that the vector z i am going to control. And since there are different groups of these controlled points (I'm planning to have more control on each of their height), I continued to split the tree until eventually all the group of points are split from the main data. And then since these created some null points, I used clean tree. After that I merge the negative of the first split, which contain all the points that are not controlled, with all of the other positive value of the splits, before connecting them to the final output mesh / surface. I still put the delauney and patch component in there in hidden mode. The file is attached below.

Thanks