This diagram is the succah from above with the front, rear and side crossmembers attached to the corner uprights (using Simpson Strong Tie metal connectors, not shown).
The Succah roof consists of 11 - 1"x2"x8' boards (lath).
This diagram shows 9 of the 1x2 boards laid across the front and rear crossmembers. The left- and right-most boards ar placed against the uprights. The others are evenly spaced about one foot apart. These boards should be placed on their narrow side to reduce sagging.
This diagram shows the remaining 2 of the 1x2 boards placed perpendicular across the others at the front and rear. These are placed on their wide side and screwed down on their ends to the top of the uprights. This will hold the other boards in place.