Every one needs a design wall - However- i was taught to also lay the quilt as it is to be used. - bed quilt on a bed, Wall hanging on a wall. the reason for this is that what looks good on a wall may not flow right/show pattern when laying flat. I speak from experience- I made a lovely 9 patch pazzaz quilt that looks great when on a wall but when laid flat on a bed you can not see the pattern at all.
Also you can use a flanel back table cloth as your design wall . I also put the table cloth on the bed/floor when laying out the top. then I just roll it up and take it to the sewing room and either hang it up or lay it on a table for sewing. This table cloth also works great to take to a class or on a retreat to carry your layed out project.