If you be here is no longer used in English, although it was fairly common in Early Modern English, around 1700, and was still in poetic and rhetorical use into the 19th century:
If music be the food of love, play on. —Shakespeare, Twelfth Night, ca. 1601
If this be treason, make the most of it! —attributed (probably falsely) to Patrick Henry, 1765
Today we use ordinary indicatives for a likely event, or irrealis past forms (with no inflection for first or third person singular) for an event regarded as merely possible, or unlikely:
If you are here it will be great. ... If he is here it will be great.
These speak of future events held to be quite possible, even probable.
If you were here it would be great. ... If he were here it would be great.
These may speak of either a present non-fact or a future doubtful possibility.
It is common in colloquial English to use Simple Past forms in the if clause alongside would in the consequence clause—If he was here it would be great—because would is no longer restricted to low probabilities. This use is now deprecated in formal English, but is likely to become acceptable over the next generation or so.