As @nmtoken wrote, you don't need to write the SQL DDL by hand. With the OSGeo Project deegree a command line tool is provided, which can generate SQL DDL statements from INSPIRE data models (typically a GML Application Schema). For example the following command generates the SQL DDL for the INSPIRE data model Cadastral Parcels 4.0 (Annex 1):
java -jar deegree-cli-utility.jar --srid=25832 --format=ddl --idtype=int http://inspire.ec.europa.eu/schemas/cp/4.0/CadastralParcels.xsd
Check the provided documentation for more information. This command line tool is intended to be used with deegree web services but the generated tables may also be accessed with QGIS or other tools. So before you start, check what kind of tools you are going to use and what you need. You may have a look on gdal driver GMLAS too.
Further information how to setup a deegree web services with PostGIS is described in the Quickstart Tutorial "INSPIRE Network Services with deegree on Docker".