Great idea for lego storage! Instead of flat surface, add lego mats. Creative Solutions for Small Space Play: Underbed Play Table with Drawers by Great Little Trading Co. (does not ship to U. but think of the DIY possibilities)
"Glow In The Dark Pathway." GENIUS…Line a pathway with rocks painted in glow in the dark paint. During the day they “charge” in the sun and in the evening they reflect the stored light. Rust-Oleum Glow in the Dark Brush-on Paint.