Bird tables are suitable for many species and most foods. Even a simple tray can be perfectly adequate, with or without a roof. It is important for the design to allow the rainwater drain away and you are able to clean away droppings and uneaten food. Sometimes elaborate designs can be difficult to clean.
Nut feeders are made of steel mesh, and are the only safe method of offering nuts to wild birds. The mesh size needs to be large enough to prevent birds damaging their beak, and small enough to prevent large pieces of nut from being taken, due to risk of choking.
Seed feeders are often in the shape of a transparent tube container with holes, through which birds are able to access the seed. These are designed for sunflower seeds and seed mixes. They attract birds such as tits, siskins and greenfinches.
Ground Feeders can be made of wood or metal. Some of them have a metal mesh protection to allow only the smaller birds in and protect them against predators.
If you are thinking of creating a home-made device as bird feeder, always consult with a reputable garden/pet shop or manufacturer of bird food for technical and safety advice.
List of PFMA members who produce wild bird food and products can be found here.
If you enjoy watching birds, consider providing more varied feeding stations to attract more species.