Timber assembly double garage leaking walls

[flixytime]

Hello. My partner has built a home assembly large timber garage. It has a good concrete base but the rain is leaking through the walls and he's tearing his hair out (or he would if he had any!).
If anyone has any useful information on how to remedy this issue, help would be gratefully received. Thanks

 

[freddiemercurystwin]

Got some photos and a link to the shed/instructions?

 

[flixytime]

Thanks for your reply. I'll ask him about photos and instructions