In a lot of homes reach in closets are common. There are no “standard” dimensions but the depth should be at least 24” in order to accommodate a hanging section. If it is less than 22” deep avoid a hanging section.
Most often a reach in closet has a header and return walls. Be sure to account for enough clearance to access that part of the closet. If standard 14” panels are used there will be only 10” of clearance to access the top shelf and the area behind the return walls.
Drawers, baskets and shelving are usually installed in the middle section so they can be fully used. Consider a 18” wide center section instead of 24” to improve accessibility for the side sections if your closet is 5’ or less.
Consider a mix of hanging and non-hanging. Usually a ratio of 70% hanging to 30% shelving seems to be the norm.
Add one smaller section for longer hanging clothes such as dresses, long skirts and suits.