For repairs and maintenance, just put all of the receipts in a folder (either on your computer or print them and put them in a folder in your filing cabinet).

Look for what the description of the unit is (where does your ownership begin, the bare walls or the studs...) and what you own inside (ie. fixures, cabinets, sheetrock, etc.). 

For example, if a house has old carpet throughout and bright yellow paint in the interior with old brown kitchen cabinets, a flipper will take out the carpet and replace it with nice tile, paint the walls a more appealing color, and repaint or insert new kitchen cabinets.

I put a fire extinguisher under the kitchen cabinet.  

We have opened up the kitchen floor plan, refurbished all the cabinets, and will redo the backyard.

Here is the actual deal I'm trying to make happen on a property that needs carpet, paint, new shower, bath flooring, kitchen cabinets.  

@Chris Bingham I help my dad with his 20 units, and he is way old school and does everything on paper and nothing electronically, and has a huge locked file cabinet full of paperwork.

From there it's the cosmetic piece with drywall finishing, paint, cabinets and flooring. 

When I worked as a construction manager for a homebuilder several years ago, we ordered the lumber, windows, doors, stairs/railings, garage doors, trim, cabinets, lighting, appliances, vanities, floors, paint, and other finishes.   

Assuming you have coverage, after deductible, depreciation of the items like cabinets, etc., your recovery will be limited.