Finding eigenvalues for Laplacian operator for 3D shape with Neumann boundary conditions

I've just begun to use the Mathematica so my question may seem to be naive. To get a solution for my problem I looked at the example provided in help.

{vals, funs} =
NDEigensystem[{-Laplacian[u[x, y], {x, y}],
DirichletCondition[u[x, y] == 0, True]},
u[x, y], {x, y} ∈ Disk[], 6];

And I tried to apply it for 3D shape like this.

Ω =
Pyramid[{{aa, aa, 0}, {aa, -aa, 0}, {-aa, -aa, 0}, {-aa, aa, 0}, {0,
0, hh}}];
Γ =
ImplicitRegion[((Abs[x] >= Abs[y] &&
z == hh*(1 - Abs[x]/aa)) || (Abs[y] >= Abs[x] &&
z == hh*(1 - Abs[y]/aa)) || z == 0), {{x, -aa, aa}, {y, -aa,
aa}, {z, 0, hh}}];
aa := 1;
hh := 1;
NDEigensystem[{-Laplacian[f[x, y, z], {x, y, z}] ==
NeumannValue[0, Element[{x, y, z}, Γ]]}, f[x, y, z],
Element[{x, y, z}, Ω], 6]

But unfortunately it returns the same thing as I have at input. Can anybody explain to me what I'm doing wrong?
I edited this post to make things more clear. I'm looking for natural frequencies of pyramid bounded area. So, my end-goal is to find eigenvalues and eigenfunctions for the Helmholtz equation with Neumann boundary condition u'[x,y,z]=0 on the surface of a pyramid. This task seemed to me to be difficult to start with so I decided to find first eigenvalues for the Laplacian operator. Here is the Helmholtz equation:

Laplacian[u(x,y,z),{x,y,z}] + k^2u(x,y,z) =0
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As shown in the docs for NDEigensystem, the proper way to specify a homogeneous boundary condition with NeumannValue is to add it to the linear operator (only homogeneous boundary conditions are supported at this time, V10.4.1).

Block[{aa = 1, hh = 1},
Ω =
Pyramid[{{aa, aa, 0}, {aa, -aa, 0}, {-aa, -aa, 0}, {-aa, aa,
0}, {0, 0, hh}}];
eigs = NDEigensystem[{-Laplacian[f[x, y, z], {x, y, z}] +
NeumannValue[0, True]}, f[x, y, z],
Element[{x, y, z}, Ω], 6]

];

Grid[Partition[ 