In addition to the usual comment about desktop being easier to upgrade than laptop -- you may want to avoid "low profile" style cases -- as they tend to severely limit the choice of I/O cards that can be added (i.e. not only are the endplates a different size, the circuit board needs to be narrower to fit). Other concerns regarding desktop are the number of I/O slots available (if get a motherboard that is mini-ITX, you may only have one I/O slot), as well as number of slots into which memory modules may be fitted. Some lower-end systems may be limited on the number of memory modules that can be fitted, or in some occasion, an absolute limit in the amount of memory that can be installed.