Haven't tested code at all, mainly you have to declare MONSTER_CLASS not as const, and may be you haven't passed a Float as radius, or you passed a Float but native wants an integer.
For other warnings, if you use amxx1.8.3 you can use write_coord_f and write_angle_f, else you can use engfunc(EngFunc_WriteCoords and engfunc(EngFunc_WriteAngle when Float args are passed.
Anyway, this is scriptin/help forum, you should be able to get rid of such warnings by yourself.