[Infinity]

Don't do what Flashy said, it's unneeded.

Addhouse is a function in the house system FS you use, so add the "addhouse(blabla)" lines under OnGameModeInit,
and add the "AddHouse(houseid, Float:iconX, Float:iconY, Float:iconZ, Float:interiorX, Float:interiorY, Float:interiorZ, Costa, Sella, Interiora, virtualworld)" function somehwere else in the script. (Not IN an other function.)
Also make sure you have the right includes.