NSIS Example using MUI2 with a custom page built with NsDialogs.

mui2-custompage-nsd.nsi

!include nsDialogs.nsh
!include LogicLib.nsh
!include MUI2.nsh

Name nsDialogs
OutFile nsDialogs.exe
RequestExecutionLevel user
ShowInstDetails show

Var Dialog
Var TextUser
Var TextPass
Var TextDbName
Var TextPgDir

Page custom pgPageCreate pgPageLeave
!insertmacro MUI_PAGE_INSTFILES

!insertmacro MUI_LANGUAGE "English"

Function pgPageCreate
    !insertmacro MUI_HEADER_TEXT "Database Settings" "Provide PostgreSQL config and install directory."

    nsDialogs::Create 1018
    Pop $Dialog

    ${If} $Dialog == error
        Abort
    ${EndIf}

    ${NSD_CreateGroupBox} 10% 10u 80% 62u "PostgreSQL Database Settings"
    Pop $0

        ${NSD_CreateLabel} 20% 26u 20% 10u "Username:"
        Pop $0

        ${NSD_CreateText} 40% 24u 40% 12u "postgres"
        Pop $TextUser

        ${NSD_CreateLabel} 20% 40u 20% 10u "Password:"
        Pop $0

        ${NSD_CreatePassword} 40% 38u 40% 12u ""
        Pop $TextPass

        ${NSD_CreateLabel} 20% 54u 20% 10u "New Database:"
        Pop $0

        ${NSD_CreateText} 40% 52u 40% 12u "mydb"
        Pop $TextDbName

    ${NSD_CreateGroupBox} 5% 86u 90% 34u "PostgreSQL Install Path"
    Pop $0

        ${NSD_CreateDirRequest} 15% 100u 49% 12u "$PROGRAMFILES64\PostgreSQL\10"
        Pop $TextPgDir

        ${NSD_CreateBrowseButton} 65% 100u 20% 12u "Browse..."
        Pop $0
        ${NSD_OnClick} $0 OnDirBrowse

    nsDialogs::Show
FunctionEnd

Function OnDirBrowse
    ${NSD_GetText} $TextPgDir $0
    nsDialogs::SelectFolderDialog "Select Postgres Directory" "$0" 
    Pop $0
    ${If} $0 != error
        ${NSD_SetText} $TextPgDir "$0"
    ${EndIf}
FunctionEnd

Function PgPageLeave
    ${NSD_GetText} $TextUser $0
    ${NSD_GetText} $TextPass $1
    ${NSD_GetText} $TextDbName $2
    ${NSD_GetText} $TextPgDir $3
    MessageBox MB_OK "User: $0, Pass: $1, Db: $2, PgDir: $3"
FunctionEnd

Section
    DetailPrint "Hello, World!"
SectionEnd