Area and Perimeter Practice:
https://ca.ixl.com/math/grade-3/perimeter
Area Practice:
http://www.homeschoolmath.net/worksheets/grade2/PDFs/Find_Area_Rectangle_Draw_Rectangle.pdf
http://www.commoncoresheets.com/Math/Area/Finding%20Area/English/8.pdf
Perimeter Practice:
http://www.homeschoolmath.net/worksheets/grade5/PDFs/Find_Area_Perimeter_Rectangular_Shapes.pdf
Here are some more advanced perimeter questions that include missing sides for shapes:
http://www.mathworksheets4kids.com/rectangle/square-perimeter-medium2.pdf