Around 50 years ago my Dad took me on a day trip to London to visit the "Schoolboys' Exhibition" - remember those anyone? As well as having a great day out and hearing a Hammond Organ for the first time (that was to set me on the path for my career in music!) I came home clutching a box containing a plastic, clip together kit of a 'Fireboat Tug' - bright green and with a 'working' fire monitor. It was powered by a 1.5v motor and I think I put it together that evening. Does this count as a 'first build'?
It soon became clear that the motor was too weedy and that the 'pump' for the fire monitor was never going to produce more than a dribble. So I put in a beefier 1.5v motor, got rid of the pump and the complicated coupling that operated the pump and/or the prop. I put in a stuffing tube, prop shaft and a brass prop from an friend's broken and unwanted wooden tug, with a flexible coupling. This was enough to have her haring around Hove Lagoon and she had more than enough oomph to pull my model yacht (sails furled, of course!). First 'rebuild', perhaps?
She was 'lost' for some time but turned up when my parents moved from a house into a flat and had a mega clear-out. I refurbished her again, but as a static model this time, replacing the now missing masts and adding a bit of detail like lifebelts and doors. She was also painted in something rather better than bright green! At the same time I 'found' my Triang 'Dawn' tug that my grandmother had bought me when I was tiny. That too was refurbished to replace broken and missing parts. Both models are now in pride of place in a display cabinet with other mementos of my childhood. 'Dawn' still gets the occasional lube of her clockwork running gear and a gentle wind up to see if she still purrs - she does!