From the top.
You need a trigger, script or WP to give your man the action to add a shed. Depending on when you want to give the player the chance to do this, you might put the command in the init or in a trigger or WP.
unitname addaction ["Place A Shed","placeshed.sqs"]
This will give the unit you name in the first part the action "Place A Shed", when used, the game will run the script "placeshed.sqs".
In the script "placeshed.sqs" you want to write;
y setpos[getpos x select 0, getpos x select 1, 0];
Y SetDir (GetDir X);
exit
Now when you use the action it will move the shed.