Preserving wood outdoors

[InterCity125]

We have an old wooden garage/shed, neglected but in generally sound condition. How do we go about preserving it inside and out, without affecting final decoration - for example the ability to stain or paint it? Are there any specific wood preservers we should use?
Thanks.

 

[oilman]

When the wood is dry, (probably next year now) put several coats of tung oil on it first. Don't know what tung oil is? Use your browser to look it up. It's the best thing since sliced bread and will waterproof the wood. I wish I had known about it 20 years ago. (Or even earlier).