Me and my brother made our own ratter and we didn't use any slabs of anything to level just made the frame put some tongue and groove where it needed to be for them laying the eggs coz they sleep on the little Perches you put In, we just painted it and put it in the garden 2 years later it's still fine, we now have 5 chickens (1 just died so we bought another 2) they recommend if your going t buy some buy at least two at once, and yeah hybrids is what we have and there quite good, usually lay every day, and really nice eggs too! Just keep the chicken house simple, build a simple frame and tongue and groove 3 sides, and a small compartment for them laying, and perches for them to sleep on, they do destroy your garden tho!! Ex battery are usually good layers and I always think its nice to give them a nice home after there ill treatment, hope this helps ratter you need any more advice just ask :) Al