This question comes up very frequently. Here’s a recent discussion:
The bottom line is that while none of us can predict when there might be a breakthrough, it is fundamentally hard for a program like SketchUp to use multiple cores. This is different from a renderer, in which separate cores can work independently on spatial sections of a scene, or a game, in which most of the work is done by the GPU.
So, at least for now, the best path is to get the computer with the best single-core performance you can afford and to load it up with the max amount of memory it can hold. Get a mid-range Nvidia GPU card (avoid Intel integrated graphics and be careful with AMD).