Raise or lower the downhill end of the string until level. Measure the distance from the string to the ground on the down hill side. The will give the slope as some many inches per ten feet. This information gives the fence all that is need to draw the fencing to scale and determine the need for changes in panel width or shape. If the fence is going on a granite slab, concrete, or earth, makes a difference in the post design.
Fences can be very open or light tight.
In cases of security screening a totally dense fence is required. Often it is wise to allow some air to flow through the fence to allow plant material on one side or the other to dry. Ins some cases some light should pass through. Select a percent opacity and fence selection can be designed and made to meet that requirement. The remaining decisions are principally aesthetic.