Short answer
Choose cloth for the places and seasons where you expect to wear these trousers. Ask the tailor about fibre, weight, weave and care for the specific options; a city's name alone does not determine the right cloth.
High-twist wool for resilience, flannel for winter, cotton–wool blends for the in-between months — pleats and cuffs decided for your line, not a trend.
The same four-season cloth palette serves Düsseldorf as Frankfurt, with a lighter jacket for the Rhine promenade and one truly dark suit for evening engagements.
The full cloth books span fresh open weaves through four-season high-twist to winter flannels and cashmere blends. Bring the tailor your calendar; the shortlist comes back two or three cloths wide.
The itinerary is a proposal: months are planned, dates and venues confirmed individually. Final quotations are confirmed in writing before you commit.