I'm curious too about the siding on the walls also, is it painted wood or a vinyl coating? I don't know what your plans are for the vent pipe next to the toilet, but it seems to be a good candidate for a free standing "table" - something with 2 sides an a flat top to hide the pipe, but easily removable and with the flat top providing a place to put stuff like an extra roll of TP or something hanging from a belt, etc.
Looks good, i'm sure he'll be pleased.