Welcome to the Bunnings Workshop community @dezion. It's sensational to have you join us, and many thanks for your question about Suntuf roofing installation.
The Suntuf 127 x 5 x 15cm Clear Corrugated Polycarbonate Wall Flashing is suitable for sealing your sheeting against a flat wall. I'd advise caulking some Sikaflex 11FC along the wall where the top edge of the flashing will meet it. The flashing can then be fixed to the wall, and it will compress against the sealant, preventing water from running down the wall and behind the flashing. It might be worth running a bead of sealant or infill strip along the top of the sheet as well as this will stop blow-back up under the flashing.
I'll include another method we've discussed before using a right angle length of aluminium and the foam infill.