Desktop Calculator for Drainage & Roofing

I'm looking for a Windows-based desktop software calculator that can handle both drainage and roofing calculations. This will be a dedicated tool for professionals in the field, so accuracy and reliability are paramount.

Ideal skills and experience for the job include:
- Proficiency in Windows desktop software development
- Experience with developing engineering calculation tools
- Strong understanding of drainage and roofing calculations
- Ability to ensure high accuracy and reliability of the software
- Good user interface design skills to make the software user-friendly