Right. When you get the stepped up basis as of the date of death, that covers everything that has happened to the property in the past. Improvements you made after that date can be added to your cost basis. And, you only add the actual cost you paid for the improvements. You don't include the value of your own labor, and you don't consider how the market value may have increased due to the improvement. Only what you actually paid for the improvement.
Repairs do NOT add to the cost basis. The difference between an improvement and a repair is that a repair restores the property to as-was condition or maintains its useful life, while an improvement extends the useful life or increases the value of the property. (Fixing a hole in the roof is a repair, replacing the roof is an improvement. You don't get tax breaks for repairs that simply keep personal property in acceptable condition, that's just part of life.)
