Edit: Sorry Kaiyanwang I totally misunderstood you and thought you were talking to me. My bad. I'm leaving the post up anyway.
I'm not sure what exactly you're trying to say here, but you've definitely mistaken my system. :) It doesn't work on gold at all.
Black Lotus is a Find DC 35 say. Find DC is something I invented, not a cost.
What this means is the Rogue says "I want black lotus poison this week".
He now rolls D20 + 27 and tries to beat 35.
Here is a table. On the left, the result of his roll. On the right, what he gets this week. I hope this makes clear my intention.
{table]Result | Number of doses
28 | 0
29 | 0
30 | 0
31 | 0
32 | 0
33 | 0
34 | 0
35 | 1
36 | 1
37 | 1
38 | 1
39 | 1
40 | 2
41 | 2
42 | 2
43 | 2
44 | 2
45 | 3
46 | 3
47 | 3[/table]