Can anybody help us build a model traffic light?

[kellyla]

My son has to build a working a traffic light that goes through the sequence(red,amber,then flashing green)for science class.We found a model one that is used for a train set but it doesnt flash green.Anybody know how we can build one(I am up for going to Home Depot to get anything we need,LOL) or a website that would be helpful?

Thanks in advance.