Um, I don't want to get in the middle of any debate but I have a suggestion for the trigger....
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Unit - Unit starts construction
(Whatever conditions you need here)
Turn on trigger (that finishes construction)
Set (triggering unit) = Builder
Set (constructing unit) = Building
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[Trigger that finishes construction.]
Time - Every 0.5 Seconds
Unit - Order Builder to repair Building
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[Finally reset the whole thing.]
Unit - Unit finishes construction
(conditions as desired)
Turn off - Trigger that finishes construction
Unit - Order unit to harvest gold
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To make it MUI, you might need to add indexing.
My apologies if this is dumb and does not help.