This seems like an ideal topic to get the Shed forum going. A couple of thoughts to ponder on.
1 A toy wooden boat suitable for kids (8-10 yrs) to assemble and float in a tub/bath.
2 A mini cold frame to sow seeds etc. Could be OK for small balcony. Construction simple timber frame with clear polythene sheet to replace conventional glass. This probably is bigger than guide lines. Is there flexibility on this?