Automatically Tracking How Much Material Is Left

basically I want to be able to keep track of how much vinyl material I have left after each order.

The process would be - When I order a roll of vinyl material I would input the colour ordered and cm ordered by selecting from drop down lists in the 'Vinyl Tracker' sheet. When a customer makes an order, I would select an item, size and colour from drop down lists in the 'Orders' sheet. Depending on what size is selected in the 'Orders' sheet, I would then like Excel to automatically update column 'Cm Remaining' in the 'Vinyl Tracker' sheet, however using the smaller number in the relative size column from 'Item Sizes' sheet.

E.g. If we take the first order:

World Map
Medium
Black - (M)

This would then refer to cell M5 in the 'Item Sizes' sheet (as 43.35 is less than 90).

I would then like the number which is retrieved to be taken away from the relevant cell in the 'Cm Ordered' column, depending on what colour was chosen in the 'Orders' sheet.

To make matters a bit more complex, obviously when any of the numbers in the 'Cm Ordered' column in sheet 'Vinyl Tracker' is 0, I will re-order the same vinyl roll and insert it into the sheet as per usual. How can I make it so that any new orders will take away from the latest instance of the same coloured vinyl?