What did you do this weekend? I built a model of Tow Mater from Disney's "Cars", that's big enough for my kid to sit in, entirely out of garbage. It was a lot of work and I may add a few more details, but here are some photos to inspire you to try it yourself. (Also, this actually took me several evenings as well as part of the weekend, so don't place unrealistic expectations on yourself to do it in a certain amount of time. Glue and paint have to dry.)
Use white glue AND masking tape wherever possible. You can also use the tape to temporarily hold pieces while the glue is drying.
Reinforce everywhere that kids might climb on, step on, sit on, or bend.
Build from the center out.
Perfection is NOT the goal - Mater is rusty, falling apart, and dented. Use banged up boxes, leave raw edges, be messy with the paint, improvise...
Use your imagination, and scissors and an exacto knife.