wil there be electric cement mixers / demolition hammers etc and how many people are working at once?

A big site with 6 large teams one per house, at work together all going at full blast all day, may need 3 phases. 
If it is a core team of  3 guys at a time plus occasional specialists doing all 6 but one after the other at a sensible pace, then actually the no of bungalows is not so important except for the duration, and as per Broadgage's answer, the biggest single load is the tea making and a microwave... So, how big is the site hut ;-)

Mike

wil there be electric cement mixers / demolition hammers etc and how many people are working at once?

A big site with 6 large teams one per house, at work together all going at full blast all day, may need 3 phases. 
If it is a core team of  3 guys at a time plus occasional specialists doing all 6 but one after the other at a sensible pace, then actually the no of bungalows is not so important except for the duration, and as per Broadgage's answer, the biggest single load is the tea making and a microwave... So, how big is the site hut ;-)

Mike