Roof is easy to maintain.
Don't wash it with any pre wax based soap.
To get creases out moisten the roof, put a moist towel over the spot you want to decrease and with a iron on low temp gently work the area till the crease comes out.
And lastly invest in a few spray bottles.
Wash the roof with water only and with a soft abrasive sponge to get out all the dirt. The wash with the convertible safe washing stuff using a that same style of sponge. Let it then start to dry out.
Seal the roof with a UV sealing softtop protector using a spray bottle and the correct dilution. Leave it in the banking sun to dry out.
BMW SOFT TOP CARE KIT
Other options
I use the BMW one because i get a free bucket.... FRee lol. No just kidding less of a hastle to just drive to BMW and get one. Autoglym i used before BMW's one and it's very decent. Still use the sponge i got with the kit 5 years ago.