"هٰذِهِ الْبِناية جَديدة وَواسِعة."
Translation:This building is new and spacious.
It depends on what you are trying to tell.
The sentence you've mentioned actually presumes that the receiver (listener) KNOWS about this building and you are telling him or her that THIS IS IT.
But in the sentence above, the speaker is telling information about the building itself that it is new and spacious. In other words, the speaker is identifying the building (the building was not known before that). I'm sure the logic works the same in English as well as in Arabic.
Why the writing is wawasiah..but it pronounced wawasaah?any rules that i dont know?
the word واسعة here is at the end of the sentence, so there is really no need to complete it with the last vowel. If, anyway, I want to add the last vowel for this adjective, it would be -tun (wási3atun) - feminine adjective referring to البناية (the building) which is a feminine word.
As for the vowel after "S" well... to me it sounds -Si- ... but I have to say also that the machine does not say it clearly as "I" sound but more like "E" i guess. Maybe that's why you hear it as -Sa-