I think I play in a similar style as you; I much prefer planning out a base beforehand (or at least, the majority of it). I usually build mountain bases, so with that in mind, I can give a short breakdown of what goes through my head when I'm designing a new layout.

1) Think about pathing. Moving around is, in my experience, the biggest time waster for pawns. Make sure that workshops are close to stockpiles that hold raw materials, and stockpiles to hold the finished products.

​

2) The next step is to get an idea of how materials are going to 'flow', so to speak, through your base. Think about what materials you are going to need and where you are going to need them. I like to have seperate workshops for different types of jobs, and I don't like putting all my workbenches together in one big room. I also like having a visual representation of things, so I'll make a 'flow chart' of each room/workstation, what materials they need, and what products they produce. Then, I try to group together the workshops and storage rooms that use the same materials. (I.e. I might have a room for steel slag storage, then a smelter, then a room for steel/plasteel storage, then component maker/smithing/machining, then weapon storage. That way, one workbench can take raw materials, create a product, then place it closeby for the next workbench to use and so on.

​

3) I make hallways that are 3 spaces wide. I've found this to be helpful when you're trying to get more than one pawn through a hallway - otherwise they slow eachother down. Also, despite only having one entrance/exit point to my mountain bases, I try to make sure there is more than one path between any given two points in my base. This way, if something (infestation, fire, etc.) prevents a pawn from taking a certain path to get to their destination, they have an alternate route. Also, if raiders somehow make it into the base, I'll have opportunities to outmaneuver and flank them instead of being constantly pushed back into an inescapable corner.

​

4) When it comes to actually deciding locations for rooms, I usually start with some plan for a defensible killbox. Like I said earlier, I usually build in mountains, and I usually have only one entrance/exit, which is where I build the killbox. Next, I work on food storage and production. Since I build in mountains, I need to take ventilation into account, so I'll run a single vent out to some secure location (usually into the killbox area) and plan my freezers so that their coolers will have access to a ventilation hallway for the heat exhaust. I try to keep my butcher and kitchen very close by, and then my dining room close to the kitchen. Next, since I'm already working with the ventilation system, I'll plan out any other storage rooms that need climate control (herbal medicine storage, hops, raw drug materials, etc.) and their respective workshops and finished product storage. I try to keep my medical bay closeby to the entrance of the base and in a relatively central location. After I have food and medicine taken care of, I'll plan out where the pawns' rooms will be. I usually try to keep my pawns' rooms centralized in the base, with some kind of open area or joy area in the middle, and relatively close to the dining area (the dining area is too far from food or pawns, they won't use it an just without a table, leading to a debuff). Then I try to plan out the rest of my workshops (stonecutters, machining, etc.) Workshops that are used more frequently go close to the middle, and I usually put the areas that are used least often around the extremities of the base. As far as prisons are concerned, I try to keep mine inside the mountain, but away from the rest of my base. I try to set prisons up with different wings comprised of several 2x3 cells with a single bed, then all the wings meat up in a rec/dining area with nutrient paste dispensers (it's much easier to have a colonist haul food to the dispenser to feed the whole prison instead of having the warden bring meals to each prisoner). I also try to have wood and herbal medicine storage closeby (for operations/peg legs/etc.).

​

5) Don't be afraid to change things! Despite your best planning, you may realize that you need more storage for something, or you need to add another workbench somewhere, or you need more bedrooms, etc. Don't worry about saving and trying to move things around a bit to get a better fit (a mod I've found very helpful for this is the blueprint mod which allows you to 'cut & paste' a room. Try different designs for rooms until you find one that works for your needs. Although each colony will be different with respect to spacing/building area restrictions, the principles of reducing hauling time and keeping workshops that use the same materials together will still apply.

I'll link a picture of an old base I made that demonstrates (I hope!) what I've said (https://www.reddit.com/r/RimWorld/comments/9mmxah/an_old_selfsufficient_mountain_base_i_made/). Some things I would change about this base are as follows:
1) More shell storage close to the mortars, and have the machining area closer to them as well to reduce shell hauling time.

2) Survival meal storage closer to the kitchen.

3) Some centralized misc. storage instead of having it all at the far right wing.

4) Hydroponics close to the vegetation freezers.

5) Larger medical bay, preferably with smaller rooms to avoid disturbed sleep penalties for sleeping patients.

6) More leather storage, and have it closer to the butcher table.

7) Bigger killbox at the central entrance to the base.

8) More mortars on the Eastern side. Having all the mortars together isn't as effective as I'd hoped - if raiders get close, they become ineffective. Also, there is a higher chance of at least one getting hit if sieges target them.

9) Max out workbench/toolbox bonuses.

Lastly, feel free to search the internet and forums for pictures of other peoples' bases to get some inspiration. If you see something cool/interesting/useful in someone's base, use that concept in your own. You don't have to copy exactly, but I find it useful to get ideas from many different places rather than just one source. That way, you can learn from the experiences of others instead of having to go through the tedious process of trial and error yourself.

I hope that was helpful in some way. Feel free to DM me if you have any questions.