Freelancing Supervision Works

Good day fellow engineers.

I do freelancing design services at paminsan-minsan may nakukuha akong short-time clients. One particular client I have, nakapagsubmit na ako ng plans. nagsubmit na rin ako ng estimate for the project, materials and labor, and part professional fee for the design.

Naitanong ni client kung paano ang magiging supervision ko for the project. One-storey project lang naman, no more than 40sqm.

Tanong ko lang, paano magiging basis ko for professional fees for supervision ng site? Can I propose bi-monthly payment? or per appearance?

Any insights may be found helpful. Thank you!