Research the main plants you wlsh to grow. If you are fortunate to live in Caid or Meridies, you have an advantage of having a climate that can accept a large variety of period species and further, they will be perennial rather than annual. Research the pattern style that is pleasing to you and adapt it to your needs. In dry climates, sink the garden a few feet below the general level of the surrounding yard and slope it so that precious rainfall pools in it. If you have poor drainage and lots of rainfall, mound the beds up.
Good drainage is essential to almost every period herb species.
Design your pathways so that any bedding area can be worked comfortably without having to get into the bedded areas. That is one of the main reasons this kind of garden evolved in the first place. Each very special and valuable plant in these gardens got the care it required to bountifully produce its product. One must realize that herbs and spices in period times were wealth, health and substanance not merely for taste. If you decide to rely on gravel or even grass paths, make sure that your paths are at least 30 inches wide.