The only free and comprehensive online etymological dictionary of the Spanish language
techo m. (Noun) "roof"
Very early 13th cent. From Latin tectum 'id.,' from tegere "to cover." From Proto-Italic *teg-e/o- 'id.,' from Proto-Indo-European *(s)teg-e/o- 'id.,' but the earlier form was *(s)teg- without the thematic vowel.
Indo-European
Romance
Asturian techu, Portuguese teto, Galician teito, French toit, Italian tetto
Celtic
Old Irish tech "house," Old Welsh tig 'id.,' Old Breton bou-tig "stable," Old Cornish ti "house"
Germanic
Old Norse þak "roof," Old High German dach 'id.,' Old English þæc 'id.'
Balto-Slavic
Old Prussian stogis "roof," Lithuanian stógas 'id.,' Latvian stâgs 'id.'
Hellenic
Ancient Greek τέγος (tégos) "roof"

"[In Indo-European society] roofs were thatched; words for 'roof' in some IE languages are cognate with words for 'thatch' in others, all of them derived from a verbal root meaning 'to cover.'" ~ B. Fortson, Indo-European Language and Culture (2011)