I generated the next DEM abd Orthomosaic and I am interested in extract the highest point of each building, is there any workwflow that I could implement in QGIS or SAGAGIS
I think the function you are looking for is "Grid Statistics for Polygons"
However, to get there you need Polygon Features of your buildings. If you don't have them already (you can probably get them from your local administration), the easiest way probably is to digitize your buildings in QGIS.
If you a.) don't have your buildings boundaries as vector data and b.) need to do this not only for one image but for many, you need to "detect" your buildings automatically, which could be, depending on your data, a more complicated task. In this case, a slope based Raster Filter could probably do the trick, see: Is there an automatic way to find buildings in a raster file?