Hi Robby42,
Y-tong is a brand name (ore how do you say it in English) the one miszt is talking about is from a different brand, that is why it look different from color.
But yes it depends on the size of the block, here in Belgium they are always 600*250 only how tick they are is different, from 50mm - 365mm.
They are not have but i can not give you the weight.
For making a nest i always keep in mind how big the ants is, the bigger the ant the larger i make the tunnels and rooms.

Also the how deep you make the tunnels and rooms. For
Messor sp i would take a block that is 70mm thick so you can make the rooms a 3cm deep.