Correction ... 1m high!!!

You will need up to 32 cubic meters of material (stone, soil and grit) in total. It will actually be less than this because the structure will slope inwards as it goes up, so say half to two thirds of the 32. A builders bulk bag of sand holds 1 tonne and is slightly less than 1 cu.m. in volume - soil will be similar. Stones will take up a much larger volume per tonne because they have an irregular shape and there are large air gaps in between them.
In other words, Avkg, a lot but it is difficult to calculate a precise quantity.

Wow, how brilliant are you B.

Thanks, G ;-))))))

Thank you bulbaholic, and for such a speedy response too! I am trying to avoid too many delivery charges, so ... following your logic ... how does an initial 2 cubic metre of top soil sound? I also have one cubic metre of garden compost available to mix in. Any extra can then be added to holes/gaps for the plants as we go along during the season. Or does this sound on the low side? Perhaps 4 cubic metres soil plus one of garden compost? I have been told that once it is watered-in and flattened by upper layers, you need to double what you think is needed??

If your rockery is going to be an approximatly rectangular shape above the surrounding soil level you have nowhere near enough material Avkg47. Bulbaholic calculates you need 32 cubic metres if it is going to be 4m deep and 8m wide at the top as well as the bottom. It will probably taper in in all 3 directions, so you could guess that you'll need about 20 - 24 cubic metres.

What you're suggesting is about 3 cubic metres to surround and support the rubble and malvern stone (and we don't know how much of those 2 constituents you have).

Unless you have a heroic amount of rubble for the inside of the rockery and an awful lot of stone, I would think that you'll need a lot more material.

A, think of two builders bulk bags, a large car trailer or a small truck load, all baot two cu.m., is this likely to be nearly enough? The quantities/ratios of stone and compost will depend on what is most available cheaply. Our weather forcast is for a bad day tomorrow so I will try to put up a short blog from one of our talks about how we build rockeries. This might help.

If it is going to be a rockery it wants to be low fertility as most rockery plants grow on less fertile land!! For a start use sub soil underneath - a lot cheaper - should be some around free for collection. Then think carefully about the composition of the 'topsoil'. It would want to be a loam - but you might want one end to be acidic - for those plants that like moorland uplands, then the other end more alkaline for the chalky upland plants. Consult with the gardener what plants they intend or want to grow - and then tailor the soil accordingly.
Funnily enough, the very first garden area i created was an 'acid' bed for what i thought were rockery plants. Now 20 years later, three conifers of 30 foot, 20 foot and 10 foot screen my neighbours and the luscious spreading conifer is 20 foot wide and pruned a lot! A few of the heathers survive and there is a lovely display of cyclamen! Heyho!

Thank you so much everyone! I have loads and loads of malvern stone (a pile about 3m sq) but very little rubble - a wheelbarrow of broken bricks and such, and will get more. Thank you, Hoya, for the soil ph suggestions - never gave it a thought as I have been concentrating on the build. Your advice has given me some ideas for plants I would not otherwise have thought of. Thank you all round. I may yet come back and ask more ...