Is it possible to roll rehab cost into your loan when purchasing an investment property?
Yes,
There are several different types of rehab loans.
Bank loans, where you may need to put down 15-20%.
Conventional rehab loans offered through mortgage lenders. Usually these will be a construction loan which modifies into your end loan (arm/fixed) when finished.
Hard money rehab loans. Quick, very easy qualifications, more expensive but usually can be done with no money out of pocket except for appraisal.