Adding to existing garage slab

[crispy]

I have an existing concrete slab of approx 6x3m and I want extend it on three sides to 9x5m. I'm not sure on thickness as I haven't dug down all around it yet. I want to build a concrete panel garage on it and each 600mm wide panel weighs about 80kg. Roof will be minimal trusses and insulated roof panels, so relatively lightweight. 

 

Is the best way to extend it as follows:

dig down to solid ground,

add layer of compacted hardcore,

layer of mot,

rebar fixed horizontally into slab and tied to mesh,

then layer of new concrete poured up to existing floor level.

 

Could anyone suggest companies who have done this type of job, or ballpark figure for doing it.

I'm in Hertfordshire, site access is ok although a concrete mixer truck would have to temporarily block the residential road while delivering/ pumping 12m to the area.

 

Thanks in advance. 

[crispy]

I'm still looking (and planning) this job, but haven't got any further with what to do. Any suggestions now the sun is out?