How can i convert point cloud into a predefined model in place to draw it automatically and show the changes instantaneously in the model using Dynamo ?
Short answer - you can’t.
Long answer. The best way to do this is by approximating the geometry to a mesh using dedicated custom packages/tools.
The only package I know in dynamo for point clouds is sastrugi and as far as I know it can’t do this sort of thing, at least not automatically.
Rhino and grasshopper have some tools that can do this to some degree using voxelization and mesh approximation/shrink wrapping but it is complex. Rhino inside can then bring these meshes (sometimes) into revit as a direct mesh.
Look into sastrugi and volvox for grasshopper as a starting point.