Consultancies can provide a good income, have little overheads but you must know what you are doing, and be able to do the job you consult on, to spot bad work being done
I ran an alarm/intercom/access control/locksmith/cctv business for 38 years and had hands-on experience in all of them
I now visit homes and flats in construction and advise the developer what options are available, arrange suitable quotations, vet them (sort out the bs from the true) and if necessary make sure the jobs are proceeding properly
For a full access control and security consultation, say on a 12 unit apartment block it would be R 10 000, if I have to supervise the contractors (and they without fail all require supervision) it is R 5000 per month per contractor, but I do not take on more than 2. You need to develop a good rapport with the builder and persuade him that you are here to assist, not to look over his shoulder. Of the several hundred builders I have met, I would say 3 are good ones, the others manage, just and the rest go from useless to ok on a good day (when everyone turns up)