I wonder if this has to do with the game "jenga" and how it was named? It may help some people to remember this verb if they think of that game!
The creator of Jenga!, Leslie Scott, grew up speaking Swahili in East Africa. When he created the game he did not want to call it an English name, so he named it Jenga, derived from the Swahili word for build.
Just adding to the discussion toilet / toilets / lavatory / (bathroom?): In Tanzania the word 'Msala' (mi-) is often used: enda msalani = go to the toilet.
"We are building a lavatory" was not accepted, but it's one of the meanings given for "choo." Is there a distinction?
Nope. Lavatory should be accepted; report it and the error will be fixed. As a general guideline, double check Duolingo's dictionary with another dictionary like Wiktionary if you aren't sure. Occasionally the sentence is right but the dictionary is wrong.
Swahili is made up of noun classes and agreements. "Choo" belongs to the "Ki-Vi" noun class.
The singular form is choo.
The plural form is vyoo
Tunajenga vyoo = We are building toilets
Precisely! Why not toilets? Also, according to the dictionary, "shamba" is not only a "farm", but also a "field", which is probably why the word is illustrated in one case with the photo of what looks like a sports field. No doubt in due course of evolution these little matters will be cured. .
Choo is singular. If it were toilets, it would be vyoo.
Because CHOO is singular, TUNAJENGA CHOO translates as WE BUILD TOILET which is not correct English. As has oft been pointed out, the plural of choo is vyoo. I don't know how you would translate "We are building a toilet." or for that matter: "We build toilets, (but at present we have no work) .