Thanks for the advice guys. I'll let you know how I get on. I appreciate it's not going to be amazing but I have a sheltered garden and will treat the wood again first before putting it up. Money is a premium at the moment and if this sees me through 5 years I'll be happy.
To those looking for a good deal on a shed ASK AT B&Q about end of lines That`s what I did..Got a shed for £50.. Also got their smallest one for a tenner. I think they sell it for £110 normally.
It isn't shiplap, it is overlap. Shiplap is fine but overlap is very poor as the boards tend to warp leaving gaping gaps. Also it has horrid cheap compressed board for the roof and floor.
The BillyOh Budget Overlap Store Shed is not the same there are no windows. Interestingly it does have a 10 year guarantee so it is not going to fall apart in a couple of years as suggested in other posts.
MintyMat:
Again, thanks for the advice guys. Glad to hear your shed wisdom!