Best material for flip

[YiBing T.]

Hello BP community I just bought a 2200 square feet single family home in Baltimore City. My wife and I are planning to flip this house. This is our first big project like this. We would like to get your opinion on choosing building materials. Hearing from several investor friends to be careful not to "over renovate". I'd like to get your opinion to know what would be just right renovation? Meaning the cost of upgrades would be able to equate to the future ROI. We are having a hard time narrowing down the grade of material that would help resale value. What's your opinion on it and would you recommend where to look for building materials besides the regular home depot and Lowes in the Baltimore MD area? Thank you all in advance.