As noted in the DMG, scribing a scroll is similar to an enchantment in that each spell will require different components to scribe it into a scroll. In order to scribe a scroll, a magic-user needs three things: papyrus/parchment/paper, some form of ink, and a quill. If the scribing of the scroll is incorrect, all of the materials used are wasted. While each spell will have different requirements in terms of ink and quill, the same spell will always used the same ingredients; it is not different for every single scroll you ever scribe. At any rate, a magic-user must be of at least 9th level before they are powerful enough to scribe scrolls.
The paper, parchment or papyrus used is the most static part of the scroll. It must be of the highest quality with as little graining or imperfection as possible. A scroll made of paper has a +5% chance of success, while a scroll made of papyrus has a -5% chance of success.
The ink is always costly and difficult to produce, and as a rule is different for each spell. The ink is always some fluid that - like a spell component - bears some empathic link specific to the nature of the spell. For spells that do have a material component, the ink may be related to that component - for example, an Identify spell may require an ink produced with crushed pearls. Otherwise the ink is related to the spell itself; a spell of illusion may require ink produced from pixie dust, for example. Magic-users have written treatises and glossaries on the magical nature of substances found in the natural world, and for the production of scrolls these are essential to a wizard's library. One notable "wild card" in the case of scroll ink if the blood of a dragon. Dragon's blood is inherently very magical, and in addition to its alchemical uses it can be substituted for ink in all but the most powerful scrolls.
The quill is also specific to the spell. Each scroll must be scribed with a freshly cut quill that has never before been used. The cutting of the quill must be fine to ensure that no ink is splattered or wasted and the quill does not split. The quill is specific to the spell - for example, the feather of a cockatrice for a scroll of Stone to Flesh. A quill that was harvested personally by the mage who is scribing the scroll confers a +5% chance of success.
Once the ingredients are gathered together, the magic-user may begin the process of scribing, which takes one full day per level of the spell being scribed. Regardless of whether or not the scribing is successful, all of the materials are consumed by the process. There is a base 70% chance of success, which can be modified by the quill and type of paper being used. For every level of the spell being scribed, 1% is subtracted from the chance of success. However, each level of the spell caster adds 1% to the chance of success.