This is for drainage pit. I have been trying to incorporate IF and
sumproduct(-- statements and I can't seem to get it right. (Maybe I need to
write a program?)

I have a large number of pits which will be made up of a combination of a
base piece and a number of riser components to make up the height required.
The minimum width of pit is determined by the largest pipe to it, according
to; Pipe Dia<=450 then min. width=670 and Pipe Dia450 then min.
width=670+200(mm).

Prices are for pieces in standard sizes, as follows.
750 (pit width):
Base=900mm(depth)=$a
Risers=600mm=$b
Risers=300mm=$c
Risers=150mm=$d

900 (pit width):
Base=1200(depth)=$w
Risers=600mm=$x
Risers=300mm=$y
Risers=150mm=$z
etc.

All bases are either 900 or 1200 deep.
All pits will require a base and at least 1 riser (as all pit depths greater
than 1200mm (presumably easier then to leave out base in pit height calc)
Spreadsheet has been set up accordingly.

Eg. Pit depth = 1600mm and largest pipe = 500mm.
Therefore, need:
- pit with greater than 700mm so use 750 pit.
- 1 base+2 risers (900+600+1500=1650)
- output price (one pit) = $(a+b+d)

I hope this makes sense, let me know if you need any more info.
I know this is longwinded, but any help would be greatly appreciated; I've
seen the answers on this site and I'm sure one of you can do this!