Landscaping industry - working capital

Nearing LOI at the moment on a landscaping firm. The business model is doing new project installs for new build housing firms.
Headline price acceptable, but we need to determine the normalized working capital.

Owner is concerned that the offer might be adjusted downward too much if working capital adjustment clause comes into play, leading to his min expected outcome not being met.

Business based in the UK. Anybody here able to provide advice on what the typical working capital requirements are for this kind of landscaping firm?