I'm writing another Starfinder Adventure Path adventure. It's not announced yet, but I don't think I'm doing the company any harm by saying I'm writing for them again. I don't think anyone is betting that Starfinder is going to quit doing Adventure Paths, or that they're going to quit arranging for and assigning them behind the scenes, before a public announcement. So I can't yet say what it is, I can say I'm writing a Starfinder adventure.

I just turned in my milestone--about half my total word count--and I had a strange experience in doing so that I took as a good lesson for future adventure writing.

My adventure requires a somewhat complicated subsystem. Not all adventures do, but this one does, and I was told about it from the outset. I'm not writing that subsystem, although I've had some input on it, and I'm permitted to sort of flex it as I need for the story I'm telling. 

I've also agreed to write a handful of the new monsters that appear in my adventure, because some of them have some significance to the overall plot and none of the existing monsters in the Alien Archives quite fit the need.

There isn't any adventure that's written by typing from the beginning and just typing and typing and when you get to the end you're done and send it in. There's a whole lot of skipping around (as I've mentioned before, I usually write my adventure introduction last), reworking parts that don't fit, jettisoning whole blocks of text, cut and pasting from an outline or other source, and so on. It's like building a house; you start with an existing foundation, you make a good but maybe not quite perfect frame, then you do everything else to build the house: finish out the windows, erect some walls, and maybe you do part of the roof somewhere in the middle there because you want to keep the walls apart while you're working on them, and so on.

The existing rules and lore are your foundation, your initial outline is the frame, and writing the adventure is like building the rest of the house. Let's take these one at a time, and backwards, because the foundation is the thing I really want to focus on.

Building the House. This is the bulk of your adventure writing, and it's the thing that's most visible to anyone playing it. This needs to be pretty as well as functional, and it will all fall apart if your frame and foundation are insufficient.

Frame. This is your outline; it's the place where you said your adventure was going to be just this big, and it's going to contain just this many encounter rooms, and so on. It's the thing your adventure is molded around; it gives it its shape, but it doesn't truly support your adventure.

The Foundation. The foundation is what gives the whole adventure its support. The foundation consists of all the pieces that need to be solidly in place so you can write the adventure. The existing game rules are an important part of the foundation, as is existing game lore. So are existing monsters you want to you use, existing items that are important to the plot, and so on. In short, all those pieces that you don't write but which make your adventure playable are its foundation. You need to take a close look at your foundation. If your adventure has a vehicle chase, you'll need good familiarity with the chase rules.

Sometimes the foundation the game gives you needs a little extra support or shoring up, and you have to create something new to do that. Perhaps the "something new" is a twist on the normal way to run an encounter ("in this encounter, the heroes' Charisma modifiers add to their ACs because the enemy is throwing witty verbal barbs.") or new rules items ("the masklords wear the following new magical masks to share their powers and see through each other's eyes, so when the Minor Masklord is killed, the Major Masklord already knows a bit about the heroes and their tactics.") or a new site or person detailed in game ("the spaceport of Sarvolven has the following key NPCs and locations in it...").

Just about every time an adventure author writes something other than the adventure, it's because that writer is the best person to build that new piece of the foundation necessary to make the adventure work.

I had expected to need to shore up the foundation for my adventure. Specifically, I expected my adventure's foundation to rely on that new subsystem that permeates it (the subsystem I didn't write). It'll be at the forefront of players' and gamemasters' minds during play, after all, so I expected it would have to be at the front of my mind, too. I'd have to learn it backwards and forwards and maybe sand off some edges or otherwise contort it to be the foundation of my house. I built in a few extra hours in my writing schedule to accommodate building and laying down those metaphorical bricks into my foundation.

Except...I didn't have to. My adventure touches on the subsystem in a few clever places, but the subsystem is really running behind the scenes the whole time. I didn't have to do much with it at all.

What I did have to build as my foundation were, to my surprise, my monsters. It turned out that having just the right monsters to fit the story I was trying to tell wasn't quite enough. I needed to know that, for example, the monster dissolved into a puddle of acid when it died, because the heroes exploring a mysterious murder site find acid burns in the floor of a room leading to the room below. How big the hole was depends on how big the new monster was, and so the new monster has to be such-and-such size and shape. And it killed the person with slashing claws, so I know it's got those, too...and, eventually, I realized I was dancing around the thing I really needed to do, which was to just build the monster.

This turned out to be the case with four of my five monsters, just to get to my "halfway done" milestone stage. Fortunately, I'd already budgeted in some time to lay a foundation, so I had the time I needed to design and build those monsters. Each one was its own brick. They were the bricks I'd needed to do my writing, after all.

The takeaway from all this is to be mindful of the foundation you'll need to create so your adventure. You'll be best served budgeting in some extra time to make the bricks you'll need. But stay flexible, and realize that the foundation you thought you might need might, in fact, be something you don't need after all; and the foundation you thought you could put off until later might become very vital to your adventure writing. Plan to have to build some bricks, but be aware the bricks you need different bricks than the bricks you think you need.