This is what started it all. We began in November 2016. Then my son received a LEGO Space Shuttle kit for Christmas, and it gave me some better ideas for the first stage booster. Weeks later, I discovered someone had already built a Falcon 9. Major kudos @reprage! At first I thought we'd build it as-is and move on to some other project, but then I realized it didn't quite meet my goals. So I used it as a starting point.
Here's my LEGO Falcon 9 design, including first stage, second stage, interstage adapter, and landing leg struts. See the Payloads section for what to put on top, since there are so many options.
Here are detailed pointers for building each component, in visual form. Click on any picture to enlarge it.
Probably my biggest contributions to @reprage's design are that I rotated the grid fins and landing legs 45 degrees from the main coordinate system of the rocket -- as they are in real life -- and I reduced the sizes of the grid fins. This enabled me to build a much more realistic Falcon Heavy. Why does this matter for my Falcon 9 model? It's in keeping with SpaceX's stated plans to have only 2 versions of the first-stage booster core in production once the Falcon Heavy starts flying. In real life, the Falcon 9 "single stick" booster cores are interchangeable with the Falcon Heavy side booster cores. So are mine!
The difference between the launch-ready first-stage boosters and the landed versions is only the addition of the black landing leg struts. No need to build a different version of the booster. Just add or remove the struts to switch back and forth.
In a couple of spots LDD didn't recognize my joints as legal, even though in real life the parts fit nicely. So I've left them hovering on top of each other. Just remember, if two pieces look like they should be pushed together, do it!
For color realism, all of the engine nozzles should be in the LEGO metallic silver color instead of medium stone gray. But the metallic ones are rare and pricey, especially considering the first stage needs 9 of those 1x1 cones. If you're up to the challenge of finding them in metallic silver, go for it!
In several places I have plugged unused holes in the 4x4 round pieces with white half-pin pieces. This is totally optional. These pins are rather expensive compared to other colors. You could easily leave them out or swap them for medium stone gray versions, at the sacrifice of some realism.
I've seen some ideas for decals on the Interwebs, but I haven't dug into them yet. I've heard you can get transparent decal sheets suitable for printing your own. I'll update this section when I have more to share.
Thank you @reprage (Clinton Freeman) for the out-of-this-world LEGO Falcon 9 model which I used as a starting point for all of this. Without your work, it would have taken me way longer to come up with these designs, and they probably wouldn't have turned out as good.