Lean to questions (base and flashing)

Hi all, I have 3 questions regarding a lean to I'm building.

It will be going on the side of my house with a corrugated plastic roof (the cheaper wavy stuff as opposed to the £30/sheet flat perspex) and a tImber frame fully cladded. It will be going beyond my fence but still on my land, however, it drops off quite a bit.

Question 1:
For the timber posts, what would be better,
-dig out as if installing a fence post, build a concrete plinth with rebars for extra strength and use bolt down post holders
-use the spike style post holders that knock into the ground (either just knocked in or cemented in)

Question 2:
Leveling the base (currently i have a flagged pathway which I intend to keep, then a relatively flat soil/grass area, then the fence, then steep drop off) do I:

A) bring it all level to the path with concrete (it would take an awful lot)

B) make a timber sub base and cover it with OSB or decking boards (easiest option)

C) kill 2 birds with one stone and build a retaining wall, fill with MOT type 1 hardcore then a layer of concrete

I'm looking for a relatively cheap option but one that will last a good while


And the final question, what type of flashing should I use and how is it attached? (Self adhesive/heated with blow torch/warmed with hot air gun just to take the shape?)

Thank you for taking the time to read and thank you in advance for any input.

Mike

The ground slopes are a problem, you have to make sure that ground water from rain does not pool up and run under the walls and that the top soil is not slowly sliding down the bank. Movement which you can not see in a grassed bank could drag your side wall out by 1/4" a year.
The other problem is splash back, water running down the side of the shed will hit the ground and bounce about, this can cause the floor to rot from the underneath at its outer edges. This is normally overcome by sitting the shed on bearers so it sits up higher then the ground under it, so the air flow also helps to dry the timber out.
I would dig out and bury a 9" X 9" X 18" block on end every yard or so, sit them on proper mortar so their tops are level. Then build the side wall with a wall plate at the top and bottom. Use some form of DPC between the blocks and the wood. Drill and plug the blocks and screw the wall plate to them. This will also give you and "edge" on which you can rest your floor joists. The floor joist will need supporting every yard or so, flagstones with mortar will do (+DPC!). Set the edges of the blocks slightly in from the wall plate edge and when you plank start the first plank so it overlaps the bottom of the wall plate by about 1/2 -1". this is so water drips off below the wall plate.
Corrugated plastic is a pain to fit, cos' you can keep on tightening the screws and as you do the corrugations flatten out and the sheet gets wider. The way I did it which was very neat (and expensive) was to put the sheet down on a flat surface. Carefully adjust it so the overall all width corresponds to the label. Carefully measure the gap between the surface and the underneath of a ridge. Now what you need to do is to manfacture spacers that are the same height. For my mini corugated stuff I found that 22mm copper pipe was right, so I cut up 50 bits 1" long with a clearance hole through its diameter. So these were used as spacers and the screws tightened just until the pipe was trapped. I suppose if you were clever you could make a jig, which you extricate after tightening a screw. The other thing is that the flashbanding, you can make it water tight but it will not be neat. Check that you can buy the correct corrugation to flat transition pieces, they are expensive but give you a flat surface to flash band to, and are worth it.
My $.02 worth.
Frank

Excellent advice, thank you very much! How deep should I make the mortar bed for the blocks?

When you say "wall plate" do you mean a piece of timber running right along? And all the blocks should finish slightly inside the structure to stop water gathering around the timber?

Excellent tip regarding the corrugated plastic!

Is the flashing you describe in strips as opposed to on a roll? I don't think I've seen any profiled flashing?

Kind regards,
Mike