IF statement with matched results

[KirstAnn]

So I think I need an if statement but I cannot seem to make it work but here is my problem (hopefully I can explain it well enough)

Colum A is a number (meters squared of work completed)
Colum B is size of rock used (naming convention used through drop down box being used a total of 5 variables)
Colum C is size of rock used (sometimes more than one size is used again with same naming conventions but never are there 2 cells with the same rock repeated)

In Colum D I want to total the amount of square meters a particular rock sized has been used.

So along the lines of for cell D1 I’m trying to solve IF B1=ROCK7 then D1=A1, if no result matched check cell C1 for ROCK7, if matched then D1=A1, if no result in B1 or C1 then leave blank

Thanks in advance

 

[t0azt]

=if(or(b1="rock7",c1="rock7"),a1,"")

 

[KirstAnn]

Thank-you worked perfictly once I translated it to correct cells