I charge a flat fee for a performance costume, do I need to pay the State of Indiana sales/use tax on the purchases that I make from the different costume companies?

If you are asking do you have to pay each supplier you order from the answer is yes. Each one of them must charge the tax.

Do you work in a percentage of the tax when you sell a costume you have made from materials you have purchased ?

If you have to report to the state, the you should account for it.

We order a variety of costumes from different companies and they are various prices. We charge $65 for an adult costume & $60 for a child costume no matter how much we pay for the actual costume. We should still pay the sales tax on the amount that we paid the costume company?

Are they invoicing you sales tax ?

No, the supplier does not charge sales tax.

Then it is likely you are being treated by the supplier as a wholesale buyer and thus are exempt from sales taxes.

You need to contact the Indiana state tax department to find out if you are required to charge sales taxes.

Not sure I fully understand your question but here is the basic way it works:

You have a state tax number I assume? I also assume you are in Indiana since you mention it.

You buy from a supplier...you sell to a customer. If you sell to a customer in your state, you need to charge state sales tax to that customer for the price you sold the item for, not what you purchased it for. You then turn that sales tax that you collected to the state at a pre-determined time (3 months, 6 months...whatever is required).