How to build large deck on sloping ground?

[Minyarra]

Hello

I am looking to build a deck at the front of our home which is a converted steel shed on concrete slab. The deck is quite large 12m x 5m overall and it sits under a pergola that has just been completed. (see attached drawings and images.)The pergola posts (150x150) are shown in pink. the dimension pointed to the posts is the height of deck from ground level. 

I am concerned mainly about the deck's height from the ground which at the lowest point would only be about 160mm and at its highest point 885mm (this is fine; I will do steps at this section).

The lowest point, being 160mm from ground to top of deck leaves only 140mm for bearers and joists, with the bearer sitting on the ground (using a 140mm bearer) and the joists flush to the top of the bearer. I expect that I need the bearer to be a minimum of 75mm from the ground.

Is that correct? 

What should I do to make this workable? 

Is a 140x45mm H3 timber bearer suitable? or should I go to a steel purlin/box section?  

Should I dig it all out to increase the space underneath? how much?

about the number of stumps 

[Minyarra]

thanks @Dave-1 

This is my first deck also, so I am nervous about wrecking a few $'000 worth of timber 😅

Thanks for your advice; I will be trialling screws driven in at an angle with pre-drilled counter-sink

[Nailbag]

Hi @Minyarra 

Ignore the photo as it was a screenshot I took off Google to show the screw angles. The image below better shows the board cuts are 90deg finishing dead centre of the joist as @JacobZ also mentioned. Refer to this image below.

Also, I highly recommend using a product like Protectadeck if your not already to increase the life of the deck boards and joists from rot. The black line on top of the joist is where it sits. The boards and screws hold it in place.

Nailbag