Complex sentence: Some of the local residents in neighbouring streets would profit by turning their yards into a makeshift car park and charge speedway patrons to park there.Some either watched the action for free from their roof tops or would erect small grandstands for friends to also watch for free.
Split into simpler sentences: Some of the residents overlooking the venue would profit by turning their yards into a makeshift car park and charge speedway patrons to park there. Also, some either watched the action for free from their roof tops or would erect small grandstands for friends to also watch for free.