You can pretty much take the base tasks to do this.

The Destroy Vehicles or Destroy Building task can be copied and adjusted as necessary.

The files you need:

1. \x\alive\addons\main\static\Tasks.hpp - add the following but change the word Building for whatever you want to destroy and edit as appropriate.

// Destroy Building Task

	_options = [];

	_tasksData = [] call ALIVE_fnc_hashCreate;

	_taskData = [] call ALIVE_fnc_hashCreate;
	[_taskData,"title","Destroy Building near %1"] call ALIVE_fnc_hashSet;
	[_taskData,"description","Destroy the %2 near %1!"] call ALIVE_fnc_hashSet;
	[_tasksData,"Parent",_taskData] call ALIVE_fnc_hashSet;

	_taskData = [] call ALIVE_fnc_hashCreate;
	[_taskData,"title","Destroy %1"] call ALIVE_fnc_hashSet;
	[_taskData,"description","We received intelligence about a strategically important %3 near %1! Destroy the %2!"] call ALIVE_fnc_hashSet;
	[_taskData,"chat_start",[["HQ","We received intelligence about a strategically relevant position near %1! Destroy the objective!"],["PLAYERS","Roger that"]]] call ALIVE_fnc_hashSet;
	[_taskData,"chat_success",[["PLAYERS","The objective has been destroyed!"],["HQ","Roger that, well done!"]]] call ALIVE_fnc_hashSet;
	[_taskData,"reward",["forcePool",10]] call ALIVE_fnc_hashSet;
	[_tasksData,"Destroy",_taskData] call ALIVE_fnc_hashSet;

	_options set [count _options,_tasksData];

	[ALIVE_generatedTasks, "DestroyBuilding", ["Destroy Installation",_options]] call ALIVE_fnc_hashSet;

2. Copy \x\alive\addons\mil_c2istar\tasks\fnc_taskDestroyBuilding.sqf (or DestroyVehicle) and name it fnc_taskDestroyMyThing.sqf. Edit the code as necessary

3. Update \x\alive\addons\mil_c2istar\CfgFunctions.hpp with your new fnc_taskDestroyMyThing.sqf entry.