Wide-leg trousers are back, and about time. Slim trousers were a preference of the fashion trade, never a rule of tailoring, and a lot of men wore them for a decade without ever being comfortable. A wide leg moves beautifully, drapes beautifully in decent cloth, and is far kinder to you across a long day and a longer commute. We cut them the way serious tailoring has always cut them: from the hip, with real room to move, and with the length and break adjusted to allow for the extra cloth at the hem.
How wide, and in what cloth
A wide leg needs cloth with some weight and body behind it, otherwise all that extra fullness just goes limp. A light tropical worsted can be made to work, but a medium flannel or a good wool-linen mix hangs far better and looks deliberate rather than accidental. What you are after is drape. The cloth should fall from the hip in a soft clean column instead of clinging to the leg or collecting in folds.
For our weather, a wide-leg trouser in a light linen is both practical and lovely. The extra room lets air move around the leg, which makes it noticeably cooler than a slim trouser cut from exactly the same cloth. Put it with a plain linen shirt or a linen blazer and you have one of the most relaxed and best-looking things you can wear to a daytime function in May.