Shimano Cassette 105 11-34 5800 I need easier gear but I already got 34/50 and 11-32 (11 speed edition), I read online it's possible to use long cage derailleur with 34 cog. 

Shimano doesn't make 11-34, so I was thinking of buying 11-34 from the previous edition 10 speed cassette and drop 11 and have 34,32,...,12 

Any advice on such setup? Is there a difference in the cogs width?

Jed
You can't just take a cog off a 10 speed cassette and put it on a 11 speed cassette -- the big one is attached to the spider, so you can't really remove it and use it to build your own cassette. 

There are a few options (choose one):


Use a Wolf Tooth RoadLink to mount the derailleur lower and use a bigger cassette
Use a slightly smaller front chainring (46t or 48t)
Do a cage swap from a long cage mountain derailleur
Move to SRAM shifters and derailleurs or a lower speed Shimano group (10 speed?)
Use a JTek Shiftmate 8 (or 8A, preferrably) and a Shimano 11 speed mountain derailleur and a bigger cassette
Use bar end shifters and a different derailleur
Just try SRAM's 11-36 road cassette and see if it works by adjusting the derailleur (linked article claims putting the B-screw down 2/3rds of the way makes it work fine on an Ultegra). 


I'd probably start with option (7) and failing that, opt for option (1) or (5). Other Shiftmate configurations are possible with different cassettes (e.g. 11->10 speed and then handling derailleurs+cassettes appropriately). 

Note that a 50/34 + 11-32 already gives you a pretty large range, provided you're shifting correctly.