This building is optional, it depends on you if you want it or not. 

To install it you need to drag the ymap file intro the mods > update > x64 > dlcpacks > custom maps > dlc.rpf > x64 > levels > gta5 > citye > maps > custom maps.rpf
Then drag the mapeditor file into the AutoLoadMaps folder or upload it with the mapeditor In Game.