need a new shed for 3 bikes. was gonna build one with my son. 4×4 timber frame, marine ply inner, decking board outer, nice and sturdy with a proper door and locks. got 2 y anchors to concrete in the ground, cut a small hole in the bottom of shed for huge chains to go through, inner opening door with angle iron round the frame to stop jemmying. no windows.
or buy a secure bike store…..which seem scarce to be honest.