Old carpet or sheeting over the areas you want to kill. Big deliberate wildlife area, maybe a pond. Job done. Don’t rotavate if it’s full of weeds though, every bit of chopped root will be a new weed in a matter of weeks.
Sounds like the allotment I used to have. Found a pit full of fuck knows what chemicals under the shed!Let it go wild. Then add an old settee or two, a knackered electric cooker (it must be electric), and as many old car parts and tyres as you can find.
There you go. Landscaping on the cheap.