The front of the shed is planned to be 10 blocks high at the moment.
The door opening including frame will be 9 blocks high.

So do I need a concrete lintel plus some concrete bricks for the last
course, or is there a better alternative such as wood?
The only load carried will be the roof, so in theory wood should be fine and
would also be a lot easier to fit.
The gap (double doors) is expected to be about 1624mm so the lintel would be
2000mm.