I do a far amount of business making custom stuff! It pays very well!
Do some market research for things you are familiar with and build on that.
Do some advertising around places with people that have (or think they have)disposable incomes. Think about younger single people. They love spending piles of money on useless crap that looks like it really does something!
Dont concern yourself with how practical or functional something is if its custom. If the customer wants it and can pay, build it!
I do get loads of requests for dumb stuff though that is not practical or even possible. So there are times when the request for custom has to be denied too.
One big obstacle for most people that go self employed is over coming the fact that you dont get a paycheck every two weeks.
If you can budget properly the year round income can be far greater than the regular job pay but it often feast or famine. I can make $5000 in a week and then not make anything for a month or better.
When you got money pay the essential bills far in advance. I often pay my electricity, phone, insurance, and loan payments in advance when a large payment is taken in. You wont regret it later when there is a slow time and you dont have any money to work with!
A good money making secret is to bump the design price up a bit and then offer a cash discount! That works very well. But when it comes time to pay make sure its cash. I have a few retards that cant get past the fact a check is not cash. As soon as the check book comes out tell them the deal was for cash. If they argue stick to your higher price agreement and dont back down.
The people that want to pay me with checks after they have repeatedly been told payment was to be in cash are the ones that bounce checks!
If someone pays you and wants you to hold the check take measures that it will pass the day they said it will. Find out exactly what day his paycheck gets deposited and be at his bank waiting!
His check will only pass while there is still money in the account. So let his bad check writing be someone else's problem!