2x3in or 2x4in timber (EH3 Tollcross)

I'm planning to repair and strengthen a kids climbing frame I've inherited.

Any 2x3in or 2x4in timber of modest length (1m+ and longer appreciated) or plywood/mdf would be helpful. Also roof felt, little more than a square meter.

I'm hoping someone may have some left over from construction before I go for new