Pre-Romanesque architecture has some reasonably preserved examples all over northern Spain. First example that comes to mind is a former palace, later turned into a church and hence known as Santa María del Naranco:
And its adjacent church of San Miguel de Lillo:
Both of them are in the outskirts of Oviedo, Asturias, and are most probably the best known examples of surviving architecture of the time.
As you can guess, most of the buildings left are religious (here you have the Monasterio de Suso, at La Rioja, quite characteristic)
But if you delve a little, you can find some military or civilian constructions, the most notorious probably being the Torreón de Doña Urraca, at Covarrubias (Burgos):
(The machicolations were later additions, but the structure remains essentially the same).
I'm afraid that, for regular peasants houses, as Rumacara said, common sense is your best ally.