Before designing anything, you have to have a general plan on where and how the fibers will be routed.
Lashing fiber cables to aerial poles is a very inexpensive way to build a network if you can gain access to the poles at a reasonable lease rate. Unless you are an electric co-op with your own poles, you'll need to deal with the electric utility to see if the poles are even useable (if they aren't already overloaded).
If you plan on burying your fiber, take a hard look at access ways that are dirt rather than paved road. An HOA might have legal access to a strip of grass/dirt at the side of road. Even if you have no legal access, but there are good access ways on people's properties, a community fiber network can usually gain legal easements just by asking property owners. The Michaelston-y-Fedw network simply asked property owners to allow them to trench a conduit line and they had no trouble getting all required wayleaves. Here is an example wayleave agreement that the B4RN network uses. It isn't as ironclad as a legal easement that runs with the property, but that's the kind of trade off that can make the difference between a project getting done, and one that never gets off the ground.
Also consider non traditional routes such as going along shared backyard fences. New conduits that come in from the backyard are usually easier for homwowners than having to dig new conduit around hardscape driveways coming from the front, and it also typically avoids existing buried utilities.
If you must trench in paved roads, consider using one of the many microduct products. A microduct system can be installed into a saw cut only 0.75" wide, and maybe 16" deep. These trenches are significantly cheaper to restore than a typical 3" or wider asphault trench.
To be able to trench in roads or in the utility corridors at the side of road, you generally need a license or special designation from a government entity. In the US, this may mean applying to be recognised as a Competitive Local Exchange Carrier (CLEC). Alternatively, a state franchise agreement may be all that is required.
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