Garden Shed; Wooden or Metal

It matters where you plan to put the shed. If its in view from the windows of your house than I would go for a solid wood shed. Just for aesthetics.
The metal shed would last longer but they can be ugly looking.
The metal shed needs a concrete base opposed to the wooden shed that can be simply put on blocks. I myself have a 14 by 6 wooden shed. I have it seven years and its solid as a rock. Ronsel 5 years satin clear varnish does a good job. I have seen people buy cheap lapwood sheds and after 2 years they fall apart.

The main differences are.
Wooden Sheds, on blocks, maintenance,

Steel Sheds, concrete slab, maintenance free.

many timber sheds, including mine, are in a corner or against a wall, where regular maintenance is impossible, and eventually they fall apart.

Cost, timber sheds are less expensive.

Metal sheds -- massive condensation inside unless they are dry lined and insulated. Concrete floor necessary. Otherwise, minimal maintenance. More expensive but better in the long term if insulated.

Wooden sheds -- not damp-proof and needing annual maintenance (preservatives, possibility of rot). Roofs covered with the useless roofing felt that's normally used, leaking regularly and needing replacement every few years.

I have a wooden shed that I use for general storage of junk, but it is damp and not suitable for storing expensive garden tools and equipment. I also have a steel shed that I took the trouble to fully insulate and dry-line with 9mm ply. It's as dry as a bone and it preserves my equipment well. It cost me at least twice as much as the wooden shed, but I don't have my mower and shredder etc. rusting quietly away! That, to me, is a saving.

Lucky you. The last shed I had, concrete block with metal roof - massive condensation that literally saturated everything inside so it was unusable. I now have a wood cabin. Much better in all respects except maintainance, which is worth it to me.