how do i call a person who makes doors,windows,gates etc of iron ?

Nowadays companies or brand names are normally used. Thai aluminum is referred for sliding doors/windows.gateway is used for computers etc, nowadays the brand name is in.

I believe the proper term would be blacksmith….

“A blacksmith is a person who creates objects from iron or steel by “forging” the metal; i.e., by using hand tools to hammer, bend, cut and otherwise shape it in its non-liquid form. Usually the metal is heated until it glows red or orange as part of the forging process. Blacksmiths create such products as wrought iron gates, grills, railings, light fixtures, furniture, sculpture, tools, decorative and religious items, cooking utensils and weapons. A skilled blacksmith can make a good looking product that shows skill and ingenuity with the minimum amount of work and energy.”

an “iron smith” (an older term) or an “iron worker”