「作り上げた」(tsukuriageta) is the past form of the verb 作り上げる (tsukuriageru), which means "to build, complete, achieve", often with the idea of effort or finished creation.
Let's break it down:
作る (tsukuru) = to make, to fabricate
上げる (ageru) = literally "to elevate", but in composition this can reinforce the idea of completion or elevation
作り上げる = to create entirely, to complete something with care or effort
作り上げた (tsukuriageta) = past form → built, created
So yes:
"Tsukuriageta" = "built", "completed"
The ending -ta is indeed the past form of the verb in Japanese.