As long as you do not follow the paths for your style, you go to the store owner with 50/50 – and then you can go to it. Maybe start renting at one place in the local store, set some shelf space and sell your own T-shirt with your own specific designs.
There is nothing to prevent people from serving T-shirt printing Singapore to people who want their unique design! You can take orders and design, then you can pass it to your printer. Collect them when printed, and collect cash from your customers – at a great advantage, obviously! Your USP will be that people can wear such designs that have someone else – you can also wear them in your own design!