Hi Gianluca, so often a repeating pattern like that can be best done in a rendering program using displacement texture mapping.

But if you do want to try and model it directly in MoI, then using the Flow command will be your best bet - to do that you will model the ripples as a separate object that's just oriented on a flat x/y plane, you could use control point manipulation or do a loft through a series of wiggly curves to make that base surface.

Then using the same kind of technique as that Pineapple model you could use Flow to wrap the flat wavy pattern on to your surfaces.

See here for some more info about Flow:
http://moi3d.com/forum/index.php?webtag=MOI&msg=4856.2

But if you are intending to render this object anyway it may be a lot easier to do the pattern as a displacement texture map in your rendering program instead of trying to model that kind of pattern manually.

- Michael