Thickness / size / volume of a macrophage
BioNumbers is a good database for different values (numbers) in biological systems. From BioNumbers*:

Volume of an alveolar macrophage ( Homo sapiens ) = 4990 (±174) µm3

Diameter of an alveolar macrophage ( Homo sapiens ) = 21.2 (±0.3)  µm

So, your thickness should be (assuming a circular shape of the cell):

Volume/(pi×(0.5×diameter)2) = 14.15 (±1.52) µm

Apparently, the size of the alveolar macrophages varies a lot between different species.


  The AM from humans were significantly larger (p &lt; 0.05) than those
  from all other species studied, corresponding to a 4-fold larger cell
  volume of human AM (4990 +/- 174 microns 3) compared to hamster (1328
  +/- 123 microns 3) and rat (1166 +/- 42 microns 3) AM




*
The paper that BioNumber refers to is this:  
Krombach, Fritz, et al. "Cell size of alveolar macrophages: an interspecies comparison." Environmental health perspectives 105.Suppl 5 (1997): 1261.