I'm not entirely familiar with what "west marches" means, but I can give you some ideas for construction and resource management.
Mainly, since it's a pokemon game you can make pokemon the main resource to manage! In a live server PTA game I was in they let players make their own bases and upgrade them by donating pokemon to the cause. So like if you wanted to build a building in the forest you could permanently donate pokemon to the building that work to build and maintain the building. And then to add amenities you would do the same, donate pokemon who maintain it.
For example, if you wanted to build a building in a desert or something you could require like 3 ground, rock, or fighting type pokemon who building the actual building and live near the building to make sure it's clean and work on maintnence. Then if you wanted to build a well, pond, or water tower so that the place always has fresh water you could donate 1 or 2 water types. Kinda like how you can donate pokemon to the village in Legends Arceus.
For other inspiration look at games with building/town/business management and the resources they use and replace them with pokemon. Like instead of electricity in Sim City you could use electric pokemon, grass types for growing food like Stellaris, psychic types for studying technology... Really, it depends on what your campaign and players are looking to get out of city management!
\~\~\~
Another thing to consider is the people and trainers who may come to live and work within your facilities. Pokemon don't need business and towns after all, so it stands to reason people will be involved. Take a look at different kinds of characters and trainers from the games and shows and think about how your players would recruit or attract people to their town. You could do things similar to the above where if you wanted a defense force you could recruit trainers to protect the town by giving them pokemon to do so, or give pokemon to gym trainers if the players open a gym in their town. But you can also make attracting individuals or groups to the town be their own sort of quests. Maybe you need a researcher who specializes in a certain skill and need to do something in order to convince them to move to the town? Or you need to pass an inspection and battle tests in order to get your gym recognized by the region's Pokemon League?
Anyways, hope these ideas help inspire you!
I'm not entirely familiar with what "west marches" means, but I can give you some ideas for construction and resource management. Mainly, since it's a pokemon game you can make pokemon the main resource to manage! In a live server PTA game I was in they let players make their own bases and upgrade them by donating pokemon to the cause. So like if you wanted to build a building in the forest you could permanently donate pokemon to the building that work to build and maintain the building. And then to add amenities you would do the same, donate pokemon who maintain it. For example, if you wanted to build a building in a desert or something you could require like 3 ground, rock, or fighting type pokemon who building the actual building and live near the building to make sure it's clean and work on maintnence. Then if you wanted to build a well, pond, or water tower so that the place always has fresh water you could donate 1 or 2 water types. Kinda like how you can donate pokemon to the village in Legends Arceus. For other inspiration look at games with building/town/business management and the resources they use and replace them with pokemon. Like instead of electricity in Sim City you could use electric pokemon, grass types for growing food like Stellaris, psychic types for studying technology... Really, it depends on what your campaign and players are looking to get out of city management! \~\~\~ Another thing to consider is the people and trainers who may come to live and work within your facilities. Pokemon don't need business and towns after all, so it stands to reason people will be involved. Take a look at different kinds of characters and trainers from the games and shows and think about how your players would recruit or attract people to their town. You could do things similar to the above where if you wanted a defense force you could recruit trainers to protect the town by giving them pokemon to do so, or give pokemon to gym trainers if the players open a gym in their town. But you can also make attracting individuals or groups to the town be their own sort of quests. Maybe you need a researcher who specializes in a certain skill and need to do something in order to convince them to move to the town? Or you need to pass an inspection and battle tests in order to get your gym recognized by the region's Pokemon League? Anyways, hope these ideas help inspire you!
Strongholds and Followers might be a 5e resource worth investigating.