Any project details will work. However, the more exact the specs are, the more exact our estimation will be. Here are some items that are helpful when estimating:
A list of major features
Description for each major feature
The purpose for each feature
Source code if we are not starting from scratch
Similar projects that can be referenced as an example
The desired budget and timeline for your project.
We then take these items and create user stories from them. These are small descriptions of how the software work, meant for easy and accurate collaboration. If you want your estimation to be delivered faster, consider turning your specs into user stories yourself.