Hi @MSCreationANMore ,
Firstofall, I wouldn’t buy a PC based on an experimental/beta tool like GPU lightmass, even if it’s is incredible, because they are working on an official DXR lightmass now. Anyway, probably it will take benefits from the same hardware components.
As fas as I know, for GPUL the most important thing is the GPU, so try to buy the more expensive you can (but the cheaper of its model: for example, the cheaper RTX 2070. Between the cheaper and the expensiver could be a lot of money difference, but a little performance difference). With a budget of 1200 you should be able to buy an i7 with a RTX 2070, I think. Or at least an i5. For the rest of components, you can buy the cheaper compatibles, but it’s always recommended to find a little more expensive components. The rule (usually) is easy: the more expensive it is, the better it is.
Hope it helps,
Regards!