Foundation problem - Observatory Shed

by Derek
(Wiltshire, UK)

Hi, I have a problem, perhaps someone can help. I'm looking to build a 'roll off roof observatory'. That is a shed for my telescope with a roof that rolls off. The shed and roof are no problem, it's the foundations that are leaving me scratching my head.

I have three major problems:

1. I'm on clay in the UK, which means when it isn't raining, it's about to rain, or it's just stopped raining, it might not be hard rain... but it's pretty persistent, and all the water is running over the surface of the garden.

2. I have no access for a concrete delivery truck anywhere near the proposed site.

3. With observatories, the scope must have it's own foundations, separate from the shed.. so 'raft' foundations are to be avoided.

I'm looking at some sort of trench foundation, but that means a lot of concrete and it's all got to be manhandled. I can just about get a micro digger in, it's the concrete that's the problem.

I'm starting to wonder about block foundations rather than poured concrete, just to make it all manageable. If I just build on paving slabs on the surface it will probably float away one dark and stormy night.

So, any ideas... I'm concerned blockwork foundations will 'bend' overtime distorting the shed and preventing the roof from rolling off, if I make the shed stronger, I will then have made it heavier, so risking bending the foundations and I'm back to square one.

shed size: 5.4m x 2.7x by 3.9m at the ridge (18' x 9' x 12'h)

thanks in advance

Derek

p.s. I'm a professional engineer.. electronics... feel free to get technical.