So true about the Assembly Halls, in the US anyway. They are paid for by the Circuits that use them. A building fund is set up to accumulate the $$ to get it started. The Society "might" pitch in a part, but usually not. They are built with volunteer labor and then each Circuit is charged by the WT Society to use the facility. How clever.
Similar for Kingdom Halls. The Society has a Kingdom Hall Building Fund box in each congregation. Each congregation forwards $$ to the Society monthly collected from the box. The money is pooled at headquarters and then doled out as relatively low interest loans for KH builds. Each congregation pays their loan at interest and the WT Society continues to collect contributions from the boxes as well. How clever.