Hi @cjelimo,
Welcome to the Bunnings Workshop community, it is wonderful to have you with us.
When you say landfill, do you mean an old landfill site that contains refuse, or do you mean a site that was backfilled prior to construction? What is the soil composition like? Can I trouble you for some photos and some further details?
A garden bed that works well for vegetables, flowers, and most other plants should have a minimum soil depth of around 30 centimetres. This depth provides enough room for roots to grow properly, supports good moisture retention, and reduces stress on plants during hot or dry periods.
A premium soil blend such as this Scotts Osmocote Garden Soil Premium Planting Mix would work well. You can also mix in some compost to supply nutrients and organic matter. Including a small amount of drainage material, such as coarse sand can also help to improve soil structure and prevent waterlogging, which benefits almost all plants.
If you are looking to entirely eradicate cockroaches from your house and compound, then I would suggest you need to speak with a pest control specialist. We sell cockroach baits, but large-scale pest control would likely be difficult without professional assistance.
To know the best approach with the tiles, I would need to see them. If you can upload some photos and give me a few details, I would certainly be able to assist further.
As Jason mentioned, separating your questions into different posts would certainly help so our members can assist.
Jacob
