Making a bench isn't especially difficult if you have some basic skills and a good basic tool kit. However, there are a few simple guidelines that may help you to execute your plan.
Benchtops. Hardwood is desirable. Solid hardwood is preferable to glued-up stock, but either will do. If you are to have holes for bench dogs and holdfasts, hardwood may even be essential. Maple, a common choice, is durable and plentiful.
Massive Members Mean Stability. A good workbench is rigid: If it shifts when you are hammering or sawing, it's not stiff enough and you're wasting energy. Generally, rigidity means using large-dimension (two inches or thicker) hardwood stock.
Mortise and Tenons Add Strength… The best benches are joined with mortise and tenon joints where the legs connect with the benchtop and where the stretchers link the legs.
… and Bolts Are Best. Carriage or machine bolts are preferable to nails because, over time, the wracking pressures that are inevitable in pushing and pulling on the benchtop will loosen the nails, producing wobble. Lag screws are next best. When assembling the top, glue will help, too.