If I don't have a original bottom bracket how do I find out the axle length? if I know the BB shell length?

It's dependant on the BB shell width and the chainset that you're using.

And what chainline you need to achieve!

Don't know the chain line because it's going to be single speed

You'll need to match the chainline of the cranks/crankset with the rear hub to get your chain running straight.

What are planning to run?

Have a look at Sheldon Brown if you don't believe me!!

Do believe you :P. It's going to be Deore canks with a single speed at the back on a carerra kraken frame. Surely I can get any size then adjust at the back with spacers?

Well, my approach would be to find out what chainline Shimano specify for your crankset and they should, to answer your first question, give a BB spindle length to achieve this chainline. The chainline measurement varies dependant upon whether it's a triple or double and where you happen to place your single chainring. If struggling, Sheldon Brown's website does list this but often the specific page can be a bugger to find.

The BB shell width is the least critical reference.

Then you source a hub that gives you as close to this chainline as possible and hey presto, you'll have minimal need for the use of any spacers.

This is maybe complete crap and I'm talking out of my rear but it makes sense to me!

I'm guessing if Deore they're old style hollowtech octalink cranks?

Yeah they are the old style cranks I'm going to buy later

are you using a ss wheel or a cassette wheel with a "kit" fitted ?

The latter is pretty easy to alter chainline by re-spacing at the back; former much more important to get the front bang on

(err, I think)

Not that I came on here to try and sell you anything but I do happen to have some black Octalink crank arms, an alloy SG-X 32T chainring. All in pretty good shape but not perfect by any means.

Going for a song as they're absolutely no good to me whatsoever!!

If not that's fine and good luck with it all.

Cheers.