I have found the following results: after phase to elevation, I have added elevation band (SRTM 1arcs), created linear/db for both and subtracted SRTM elevation from my output. Here it looks like:
Also, I have filtered with mean. But the height difference is pretty weird which cannot be count as Building Height. But the built-up area is clearly visible. Here is the SRTM elevation:
And the study area is:
It would be really helpful if you help me to find a way to get the building heights. Thanks again