You can already set the number of decimals in the build tools, from the Preferences floater, "Cool features" tab, "User Interface" sub-tab, "Decimals for Pos, Size and Rot parameters in the build tools" setting...
Note also, that even though the build tool displays a limited number of decimals, you can still enter more decimals than displayed (and they will be taken into account, provided the resulting change of the parameter is greater than the minimum displayable decimal; i.e., changing 8.541 to 8.5418 will not pass if you display only three decimals (minimum accountable change = 0.001), but a change from 8.530 to 8.5418 will actually set the parameter to 8.5418).