Concrete pads for the galvanised shoes would work a treat. The one I found was the first one I came across. Easy to build similar and spec your own tiles.
Having built a summerhouse last year from a tiger sheds kit I'd say if it's a self assembly kit you could build it yourself but buying wood and building from plans is a lot more difficult and time consuming.
Just had a look, tiger sheds do a log garage but no car ports I can see which is a pity as the quality and fit was very good for the money , they do make custom projects so it might be worth a phone call