Building up nearly anything with planbuild is not a problem.
What i meant is i build a large structure with planbuild.
Its completed, but later get damaged partially demolished.
(Like trolls raid)
Then its about to impossible to restore to its original state
I was hoping for a proper snap option where the ghost plan snaps to the existing same design (with missing build pieces)
What i figured out i can manually put the same ghost plan over the existing building and manually only build up the missing ones then delete the plan when fixed up.
The problem with this workaround is there are some pieces underneath other pieces i cannot manually add materials to is since the other pieces is blocking the possibility to select the plan piece

Thanks for the info

I can't offer much advice without screenshots or further context, but I'll try. When adding materials to the rune, add iron first, as that will give the rest of the build enough stability for everything to stick. Remember, it will always want to start building from the ground upwards, so make sure to add load-bearing and structural components first. Depending on how bad your build is messed up and how big it is, I would probably suggest tearing it all down, removing any unbuilt portions of the blueprint, and then replacing the blueprint and bp rune. Also remember to have all of your crafting stations close enough to the components they are required to build (forge, stonecutter, workbench, etc.).