the word (tamma) gives the sentence the past tense,but you can't use it in the second sentence.what sentence to use depends on the context .If the context tells you when the Mosque has been started to be built,then use the first sentence with (tamma) to tell when the building has been finished.

تم بناء المسجد قبل ست مئة عام almost use "tamma" for the work done ,so there the mosque already built before 600 year's but if you want to use that sentence with out tamma then you should say بُنِيَ المسجد قبل ست مئة عام بُنِيَ=> "buneya" Add Vibrio in the first letter and the hole in the end of the word but if the mosque already in front of you while you speaking then use بُنِيَ هذا المسجد قبل ست مئة عام and with tamma it will be تم بناء هذا المسجد قبل ست مئة عام or لقد تم بناء هذا المسجد قبل ست مئة عام

we use this word to informe that our job is " done "

تم = was completed ***** بُني = the passive voice of build

I don't think there is a difference in the meaning between the tow sentences.