Creating different ID from buffer using QGIS

Question

I am trying to create a buffer around buildings to create a 'green wall'. First, I dissolved all buildings in order to create a buffer only around the buildings (flat roofs). However, after creating a buffer of 0.3m there is only 1 ID number.

I would like to create different ID numbers for every building block, because I need to perform an analysis for the different buildings. I can't do it manually, because there are too many of them.

Requirements:

1. buffer around every building block (flat roof)
2. different ID numbers

Does someone have a solution to my problem?

I am working with QGIS 3.24.2.

Answer 1

After creating the difference, run multi- to singlepart, which splits your dissolved features into single geometries, then add the $id using the field calculator.

Answer 2

I think you no need to use dissolve. Directly use buffer tool and then use expersion editor to generate IDs by using $id or @row_number expersion.