A window replacement service replaces broken windows so people don’t have to go to the city to buy glass. This is a great business as you can offer a house call service and people don’t have to take measurements, buy putty and install the window themselves (some people might not feel confident to replace the glass themselves).
This business is relatively simple, buy the glass in large panes, go to the client, measure the window size and provide a quotation. If accepted, cut the glass to size and install it.
It requires relatively cheap tools (glass cutter) and supplies (putty), you can also offer frosted glass which is often used in places that require privacy such as bathrooms and toilets (or you can cover normal glass with sandblast/frosted vinyl). Toughened glass is another product you can offer that can be used in shops. Also, look out for glass job lots where you might get the glass you can use for much cheaper prices.
Another business to look out for is to supply glass to people converting shipping containers to spaza shops.