The Brew Cabin

I have a garden that is constantly wet and with the rain we are having just now it's got alot of surface water. It never dries out and my patio and brick at the bottom of my house is always wet and has moss on it. The problem is that my garden is 13m x 5m + patio area. The 13m length backs onto open land about 150m square and this land is approx .5m higher so all the rain seems to gently run into all the houses that back onto this land. Two doors down has put a drain the length of his garden at the back and it seems to work. So i was hoping to do the same and wondered if you could answer some questions.
1 could you look here at what i plan and give me your opinion link
2 I am going to use 60mm plastic pipe perforated.
3 trench will be 400mm deep 200mm wide it will have
70mm bed of pea thingy
pipe surrounded by + 70mm on top of 20mm chips type?
100mm 0f selected free draining material (what is free draining material).
100mm soil including turf.
Also membrane does that just go on top or do you put it in trench to incase everything and just fold it over before you put soil back in.
I have been told as i am connecting to the surface water system i will have to put in a silt trap, do i have to, do you need to be able to access this for cleaning. ie will i have to have another manhole next to the manhole i am going inot to access this for cleaning or do i not really need one for this size of garden.
Thanks for any help anyone can give.

The layout looks feasible, so, going through your other points...

Why 200mm wide? And won't you need to be deeper where you connect to the SW system than at the boundary with the adjoining land?

Free Draining material is any aggregate that is highly permeable. This may be gravel, sand, crushed stone, clinker, ggbs or whatever el;se is avaialable. as long as it's inert (so no limestone, chalk etc) and permeable, it'll do.

The use of a membrane is discussed and illustrated in some detail on the Land Drainage page.

A silt trap is advisable - again, this is discussed on the page mentioned above, as is the question of access.