Building a shed, barn or playhouse depends on their intended usage. Storage, barn, workshop, playhouse, office, garage, guest house is some of those taken into consideration.
The building material for the structures are normally are made of wood, aluminum, steel, vinyl siding, siding & roofing to match home. Some custom built are now available too.
Those features to take into consideration for your building are one or more of the following; loft, plywood floor on joists, concrete slab floor, electricity, plumbing, windows, roll-up doors, drywall, insulation, painted interior, flooring or carpet, deck or porch, animal stalls, ramps, cabinets, built-in shelving, others.