If you have a good map and know which building you want to photograph, check out which way it faces before setting off. West facing means sunset; east -facing means sunrise. Southerly facing buildings are photographable all day but north-facing buildings rarely see any sun, depending on the time of year and exact orbit the sun takes during the day. Some buildings may only have sun on them for afew short weeks of the year. Preparation will allow you to have a much higher success rate.