Changing cassette from 8 to 10 or 11 to meet the Shimano 105 5800 groupset
Yes, 8/9/10/11 cassettes have different cog spacing.

You have several options:


Replace freehub body to Shimano/SRAM 11 speed compatible, if hub manufacturer provides such an option. It's 1.85mm longer than 8/9/10.
Replace freehub body with Campagnolo one. The trick is that all 11 speed cassettes are cross compatible, but Campy freehub body has same width for 10/11 speeds.
Use 10 speed cassette. This blog entry states that works good enough after some derailleur and cable tension adjusment.
Use 11 speed cassette without one cog and using additional spacer.