The insurance company told me I have 50% damage. I have heard 50% damage = a new roof

You heard wrong. Insurance makes you whole. It does not enrich you.

Your homeowner's insurance is just to restore your condition as it was prior to the damage. I asked the agent in my office a very similar question yesterday and she said the magic word "restore". The insurance company may op to repair only the damaged part and nothing more. Now if you had a new roof say less than 2 years old they may op to replace the whole shebang but that is in rare cases.

It's all up to the adjuster and the insurance carrier. Each case is different and may have different outcomes.