Measure the actual dimensions of your patio or other space where the pergola will go. Also note the location of the house or other nearby structures that might bear on the design. Transfer these measurements to graph paper, converting the dimensions to an appropriate scale, such as 1/2 inch equals 1 foot.
Create the plan view. This is the aerial, or bird’s eye, view, looking straight down over the entire project. Lightly draw the outline of the roof structure first, to get an idea of the total coverage of the pergola. Mark the locations of the support posts, then the beams (and ledger board, if the pergola will attach to the house). Add the rafters, using even spacing, then add cross slats (over the rafters), if applicable. Use the grid lines on the paper to maintain the scale and keep everything square (perpendicular). Note the dimensions of all parts shown on the drawing.
Create a side elevation on another piece of paper — a straight-on side view of the structure and any related neighboring elements, such as the house. Include all dimensions. It’s also a good idea to label each part and its size; for example, “2-by-8 beam” or “4-by-4 post.” Also note any important construction details, such as anchors or footings for the posts, and joist hangers (on the ledger board) for attached pergolas. If the sides of your pergola are not identical, create a side elevation of the other side of the structure.
Create any detail drawings as needed. A detail drawing is a close-up view of any elements or features of the design that warrant specific attention. For a pergola, you might want to draw a detail of a decorative end cut on a beam or rafter.
Refine any of the drawings as needed to reflect your final plans. Call your city’s building department to learn about specific requirements for construction plans; make sure all requisite elements are included in your drawings.