Steel I-Beam & C-Purlin Sizing

I'm looking for a structural expert to provide the necessary I-beam sizes and C-purlins (30 x 50 x 14) for a residential building with a 4:12 pitch open span.

Requirements:
- Steel I-beams and C-purlins
- Open span with a 4:12 pitch
- Must include sizes for I-beams and necessary C-purlins
- Steel needs painting for corrosion resistance

Ideal Skills and Experience:
- Structural engineering background
- Experience with residential building projects
- Proficiency in steel structural design
- Knowledge of structural integrity and load-bearing requirements

Please provide detailed specifications and ensure accuracy in measurements.