Learn Finnish: Teetitkö tämän mekon? - Did you have this dress made?

Teetitkö comes from the curative verb teettää, which is derived from tehdä. Adding the curative suffix -ttaa changes the meaning from "to make" to "to have (something) made" by someone else. If you wanted to ask "Did you make this dress yourself?", you would simply use the past tense of tehdä and ask, Teitkö tämän mekon?

Can you break down the suffixes attached to the end of teetitkö?

Certainly! The base curative verb is teettää. To form the past tense, the past marker -i- steps in, changing the stem to teeti-. Then we add the personal ending -t for "you" (teetit, "you had made"), and finally attach the question clitic -kö at the very end (teetitkö, "did you have made?").

Why does teetitkö have a single -t- when the infinitive teettää has a double -tt-?

This is standard consonant gradation in action, even on derived verbs. Adding the second-person singular ending -t closes the final syllable (tee-tit). A closed syllable forces the strong grade (-tt-) to weaken to the weak grade (-t-). The question particle -kö is attached after this process and doesn't affect the gradation.