Waterproof Cabinets Under Windows

[edenstrauss 3]

My mother inlaw has a "concave" excess space just directly under a straight row of windows, which she would like to get cabinets installed to use that space for storage purposes.

However, because of the scorching, hot sun from the western facing, the exterior of the HDB flat age really fast and has cracks. As such, rain water would seep through (not from the window) but from the cement top of the concave space. As such, we'll like to install waterproof cabinets to create that storage space for her.

One contractor who specialises in aluminium doors, windows, grilles, etc, recommended installing aluminium framed sliding doors under the windows to create that storage space. However, we thought that it looks really awful, "obiang" becox those are concepts used to sliding doors under the stove (to hide things underneath the stove).

Does any body have any idea or better recommendations on contractors who does nice, waterproof cabinets?

(note: The option in getting HDB to cure the rain seepage is out so we're not reconsidering getting HDB to do anything to the weather cracks outside the flat.)