Multiple issues - Multiple IF staements with multiple answers, or other coding.

Hi inzanesrt4 and welcome to the forum

before i even begin to try and adress your questions...
PLZ PLZ PLZ...try and avoid the use of merged cells, all the do is create havoc later when trying to reference then in a formula, and the same result can be achieved by using "center across selection" under cell formatting.

also, although using those check-boxes looks impressive, the way you are doing that, you might as well do away with them and just enter X (or whatever) into the cell and bace the references on sheet1 on that

1st problem
=IF('Tab1'!B3=True,'Tab1'!B4) doesnt work because you are referencing the row below the control, not the column next to it. try this...
=IF('Wall Types'!B3=TRUE, 'Wall Types'!C3,"") - note an if statement consists of 3 parts...
=if(criteria-to-test,what-to-do-if-test=TRUE,what-to-do-if-test=FALSE)

2nd problem
actually you only have that formula in A17:A19


I have modified your worksheets somewhat, take a look at the attached and see if that is something you can work with? (I eliminated the use of the check-boxes)