I loved playing in the sand when I was a kid. I'd build roads and tunnels at the beach for my Matchbox cars or re-create Tatooine's Dune Sea from Return of the Jedi in our sandbox. Boba Fett got lost in that sandbox on several occasions, which is bound to happen to anyone who consistently falls into the mouth of the Sarlacc in the Great Pit of Carkoon. Looks like my childhood sandbox adventures were pretty nerdy.
The recent Toon Club topic was Ancient Egypt. I figure ancient Egypt was a boring place for anyone, but especially for a kid. Aside from the short-lived excitement brought on by a passing plague, there was really only one option for something to do... play with sand. Sure, Egypt's a giant sandbox and should be tons of fun, but seriously... how many times can Boba Fett get eaten? (Technically he can only be eaten once every thousand years. That's how long it takes for the Sarlacc's unfortunate captives to be painfully dissolved inside its stomach).
So I would guess that Pharaoh came up with the idea for pyramids in the enormous sandbox of his youth, and years later he had the drive to see his vision through to reality. Mostly he had the slaves to do it, but he also had the drive. Well, okay - it was the slave drivers who had the "drive"... but those were his.