This is a good basic guide for making a code shop even tho pretty much everybody has one.
Just a few things to add:
1.It doesn't hurt to have a shop buddy. basically just somebody else that runs a shop that is willing to swap codes with you to help keep your shop up to date.
2.When designing the lay out for your maze you can use certain pieces of furniture to conceal train tracks as a secret way to get through areas. I have a couple hidden in my maze if you can find them.
3.I find that having pets attracts more guests to your house.
4.Idk if I missed it but it should be noted that it will take you atleast 20k to make a decent maze/code shop. So it will take some time to actually gain revenue from your shop.