Hello @Corentin68
There are many ways to make a mesh on the surface of an object, and some might work better depending on the situation.
A Mesh Extract will allow you to convert and masking applied to the mesh into an entirely new mesh on the surface. There are many ways to apply complicated masking to an object. If your mesh has UVs, you can apply a texture to a mesh and derive masking from that. Remember that Polypaint, Polygroups, and Masking are all interchangeable and can be converted to each other, and this opens up many possibilities for complex masking.
You can draw entirely new topology on the surface of a mesh with either the Topology Brush, or the surface snapping and edge extrusion tools in ZModeler.
You can also use the new Mesh from Mask features to draw complex shapes on the surface of a mesh.
Good luck! 