Use the "Line Array" tool (a 1001bit utility). Select a 5.5" wide board. Array it across the joists with a 1/8" gap. In 3 clicks, you have realistic decking.
The "Walls & Openings" menu provides tools to quickly create multi-layered walls (brick/insulation/drywall) and subtract openings for doors and windows. It also includes a parametric column builder for timber posts, steel I-beams, and concrete pillars. sketchup plugin 1001bit
"1001bit Tools has been my go-to plugin for five years. The stair generator alone is worth the download—it handles complex winders that would take hours to model by hand. If you work in architecture, this plugin fills the gaps in native SketchUp functionality perfectly. Highly recommended for speeding up the 'boring' parts of modeling so you can focus on the design." Use the "Line Array" tool (a 1001bit utility)
Draw a rectangle on top of the slab. Use the "Wood Framing" tool. Select "Deck Joist". Set spacing to 16" OC, direction along the length. The plugin will generate all joists, rim joists, and blocking automatically. In 3 clicks, you have realistic decking