finishing attic above garage
That would depend on how good the foundation is. Normally, the foundation is adequately overbuilt that it's not a concern. The weak link in this sort of conversion is USUALLY the "attic" floor above the garage wich is typically marginal even for light storage, and far from occupancy loads, over a very long span. Bringing that up to an adequate structure is a significant project if it was not built as such from the start.