Translation:The courier carries, but does not build a building.
This is bad English. "To carry" is a transitive verb, and requires a direct object. The implication of this sentence is that the courier carries a building, which is absurd. Better English would be, "The courier carries things, but he does not build a building"; still better, "but buildings he does not build."
Yup. That's why I opened this page too. It's the second time in this course that they use a transitive verb intransitively. Carry is very rarely intransitive. The only example I can think of is "voices carry well in this auditorium." They need to correct this and say "the courier carries __ (things, letters, or packages)."
P.S. @contributors: there was no option for reporting the English sentence so I checked all three of the available options. That's my way of saying the real reason for the report is not displayed. :)
There are contexts where "to carry" is intransitive. The dictionary gives:
"If a sound carries, it can be heard a long distance away"
Why? Because it's the action of carrying that is considered too. We do not describe someone who carry something. If it was the case, it would be wrong.
In the Duolingo's sentence, it's the action that is highlighted.
Merriam Webster clearly mention that "to carry" can be a transitive verb, if you consider the action.
1: to act as a bearer
And it's the case here! To act as a bearer....
(It's a generality, a characteristic not the description of a scene.)
I agree with other commentators: this is an awkward phrase that borders on the non sequitur. I had to double check to see if I had misunderstood something. It goes to show that grammatical accuracy (which in this case is actually - and rightly - disputed by said commentators) is necessary but not sufficient in a language course.
It's not your fault that the sentence is a bit ambiguous. "Aedificium" might be nominative singular, but it doesn't make sense for buildings to build. So it's accusative singular, but even then, couriers do not carry buildings. Of course, that means that "portat" here must be intransitive - - but then again, I don't see how carrying things is related to building.
The point of Duolingo is not to be a phrasebook, which is why we get these quirky sentences so often. The idea is that by seeing those, you'll get the knack of how to build your own sentences using these patterns you've teased out of what you've read, and an English-Latin dictionary to get the meaning. And then you could say cibus paene coquitur, vīnum nōn habēmus, or Cantus magnus est, sed amīcīs (meīs) placet.
As is often the case, the French-derived 'construct' is used less frequently than its Germanic equivalent, 'build', and it usually has a more abstract meaning (that is, you build things and construct notions, ideas, theories). But it's too harsh to consider it 'wrong'. You should report your answer as being correct.