Here is a scenario for a player to construct a building, or even a city, in a 24/7 offline advancement sandbox system.
Tier 1: Local government faction (5 levels, including many quests for material rewards)
Tier 2: > township management (ditto)
Tier 3: > zoning, design & planning (ditto)
Getting to this point might require a week of time or so if the player advances no other aspect of their character. Higher tiers will include alternate path options; for instance, after completing Tier 1, alternate Tier 2 paths might include township protecion (local police), which might then lead to a career in the military, among other things.
Note that that all of the above offer a means for offline jobbing (earning money while offline).
Once one player has achieved the Tier 3 zoning, design & planning status, they are able to buy land lots or unused buildings and approve them for various purposes, such as construction of player housing, businesses, guild halls, etc. However, this requires money, so either the character must now earn money, or other guild members (or perhaps other charcters of his/her own) have specialzed in earning money. Also necessary is a character with the necessary architectural/building skills; a source for materials and craftsmanship, either learned or purchased, etc.
For example, being able to quarry stones will lead to various stonemasonry skills necessary to provide materials for a building project. Other materials/products will be necessary as per the plans/specifications provided in the building "recipe" the architect/builder character can purchase. Wood, metal and glass products will be required; then there is the issue of furnishing and decorating the structure. Of course the first character with the city planning skills can obtain the licenses necessary to operate a business or guild, as long as appropriate taxes and licensing fees are kept up to date.
Now, building anything can be accomplished over time by any single player because they can eventually master all of the skills necessary; but it can be accomplished in far less time by a coordinated team of players. Note how just advancing down a single path can provide any player with a character that has skills other players will eventually hire just so they don't have to spend their advancement time becoming a third-tier city planner or a third-tier city architect, or a 3rd-level stonemason or woodcrafter.
Now, imagine a 4th and 5th tier to such avenues that allow the construction of actual cities by advancing beyond local government and single-building architectural/building skills, and also requiring the advancing of a guild thorough various tiered requirements into a body capable of responsibly administrating the needs of a city.
Next: The 24/7 Guild Advancement System