This company; www.beastsheds.co.uk was recommended by a neighbor who was very pleased with his shed. Plan to use This company to built a 18" x 12" shed next month.
A good bike bag is here Clicky. It does depend what travelling you are doing. Bike bags on planes are a bad idea but if you have sight of it all the time (trains/cars/coach then they are fine.
As for shed if it is just bike storage how about a ketter storage bin? Whatever you decide upon you will need to cement a ground anchor to attach a lock and quality chain.