In Spain it is not normal to display the Spanish flag except on official buildings. Some people consider it as a political pro-Franco gesture. You will no more find Spanish flags on non public buildings in Castile than you will find in Catalonia. A trawl round the Spanish regions shows that the National flag is normally displayed on public buildings, and flown higher than the appropriate regional flag. Only the Basque Region appeared to eschew the National Spanish flag.
Certainly in Catalonia you will find more regional flags, but they normally display the national flag too. The Generalitat, the seat of the Catalan government, flies both flags at the same height. The Ajuntament, or Barcelona city council, on the of the same square in Barcelona, flies the flags of Catalonia, Spain and Barcelona in that order, with the Spanish flag higher.
In Madrid the flag of the Madrid Comunidad Autónoma is often flown along with the Spanish and European flags, the Spanish flag being in the middle and higher than the other two.
In Toledo, the flag of Castile-La Mancha is flown, often alongside the European and Spanish flags with the Spanish flag in the middle and higher.
In San Sebastián, the Basque flag is very widely flown on its own. Someone doing a survey found only 2 Spanish flags in San Sebastian, one on the Palacio de Justicia beside the Basque and European flags, centred and higher than the others; and the second on the main post office with the the Basque flag. The ayuntamiento and the main library flew only the municipal flag of San Sebastián.