How do you provide proof of income for rental property if you are a full time college student?

You mean as a renter, not the building owner, right?

The same way a non college student would. Tax returns, pay stubs. The only exception would be student loan documents that cover housing.

If you don't have adequate income, your parents need to cosign.

You can show your pay stubs from your employer or your tax returns if you work but receive tips in addition to your wages. If your student loans cover housing, you can show the loan documents.

you get a cosigner... parent.

Show them your two most recent pay stubs

Rental property owners must file tax returns. And those are what you use for proof of income.